Massoud Ali Mohammadi, one of Iran’s leading nuclear scientists, was assassinated in Tehran Tuesday, just two days after the top US military commander in the region announced that the Pentagon has drawn up plans to bomb Iranian nuclear sites.

The killing and the ratcheting up of military threats are indicative of the deepening international tensions over the Iranian nuclear program. While the US, Israel and other Western powers have charged Tehran with seeking to obtain a nuclear weapon, Iran has insisted repeatedly that its nuclear programs are for peaceful purposes only.

Ali Mohammadi, 50, was killed when a powerful remote-controlled bomb exploded near his vehicle as he prepared to drive to work at Tehran University. The blast shattered windows 300 feet away in Ali Mohammadi’s northern Tehran neighborhood of Qeytariyeh. It was reported that the bomb was strapped to a motorcycle.

Ali Mohammadi taught neutron nuclear physics at the university, and, according to at least one report from Iran, he was among Iranian citizens subject to international sanctions for involvement in the nuclear program.

Colleagues of the murdered professor described him as apolitical, although his name appeared with those of more than 200 other academics in a statement supporting opposition candidate Mir Hossein Mousavi’s challenge to the results of the disputed June12 presidential election, which gave President Mahmoud Ahmadinejad a second term.

Iran’s senior prosecutor charged the US and Israel with responsibility for the attack. “Given the fact that Massoud Ali Mohammadi was a nuclear scientist, the CIA and Mossad services and agents most likely have had a hand in it,” the prosecutor, Abbas Jafari Dolatabadi, told the state-run media.

Foreign ministry spokesman Ramin Mehmanparast said that initial investigations pointed to “the Zionist regime, America and their mercenaries in Iran in this terrorist incident.” He added, “Such terrorist acts and the physical elimination of the country’s nuclear scientists will certainly not stop the scientific and technological process, but will speed it up.”

Iran’s press TV commented, “It seems that kidnap and assassination of Iranian scientists is on the agenda of the United States.”

Washington brushed off the accusation. “Charges of US involvement are absurd,” said State Department spokesman Mark Toner.

Given the growing bellicosity of Washington’s threats over the Iranian nuclear program, together with the fact that the US and Israel are the leading practitioners of the criminal policy of targeted assassinations, Tehran’s charges cannot be dismissed so easily.

The state prosecutor, Dolatabadi, said that the killing of Ali-Mohammadi follows the disappearance last June of Iranian nuclear researcher Shahram Amiri during a pilgrimage to the holy city of Medina in Saudi Arabia. The Iranian government has charged that he was abducted by Saudi intelligence and handed over to the US.

The Financial Times of London also pointed to the case of Ardeshir Asgari, a professor at Shiraz University, who worked at Iran’s nuclear uranium conversion facility in Isfahan. His death in 2007, at the age of 44, was attributed to “gas suffocation,” but there are strong suspicions that he was murdered.

The US-based intelligence web site Stratfor noted: “Three years ago, a noted Iranian nuclear scientist, Ardeshir Hassanpour, was killed. At the time, Stratfor had learned that the Israeli intelligence service Mossad was behind the assassination. Indeed, even this time around, Iranian officials have pointed fingers at the Jewish state. It is, however, too early to tell if that is the case.

“Assassinations of individual scientists and even defection and kidnapping of others is not unprecedented. Furthermore, there have been bombings in recent months that have targeted senior military commanders of the country’s elite military force, the Islamic Revolutionary Guard Corps.”

In another article, Stratfor wrote that the assassination of Ali-Mohammadi will complicate negotiations between the West and Iran over the country’s nuclear program. “That could provide an opportunity for Israel,” the web site continued. “If Iran becomes more inflexible in the nuclear negotiations, Israel will have a stronger argument to make to the United States that the diplomatic course with Iran has expired. And should the United States be driven by the Israelis to admit the futility of the diplomatic course, the menu of choices in dealing with Iran could narrow considerably.”

The assassination in Tehran came just two days after the senior—and highly political—US Army general, David Petraeus, announced in a television interview that Iran’s nuclear facilities “certainly can be bombed.” Petraeus heads the US Central Command, which oversees both the Afghanistan and Iraq wars. His statement signaled a significant escalation of US military threats against Iran.

In an interview with the CNN cable news network broadcast Sunday, Petraeus declared that “it would be almost literally irresponsible” if CENTCOM (Central Command) failed to draw up “plans for a whole variety of different contingencies” relating to a potential military attack on Iran.

The general said that despite reports that Iran had dispersed its nuclear facilities and sought to protect them in underground tunnels, they can still be attacked. “Well, they certainly can be bombed,” he said in the interview. “The level of effect would vary with who it is that carries it out, what ordnance they have and what capability they can bring to bear.”

While Petraeus refused to comment on Israeli plans for military action, the statement was clearly an oblique reference to whether an attack on Iran would be carried out by Tel Aviv, which has repeatedly threatened such a strike, or the United States. The US military is accelerating production of its new “bunker buster” weapon, known as the Massive Ordnance Penetrator. This 30,000-pound bomb is reportedly capable of burrowing 200 feet into the ground before detonating.

In a statement that suggested the grand scope within which Petraeus sees his military responsibilities, the CENTCOM commander allowed that “there’s a period of time, certainly, before all this might come to a head, if you will.” In other words, he is prepared to allow the politicians and diplomats to go through the motions with Tehran before he takes charge.

Tehran issued a muted reaction to Petraeus’ provocative remarks. A foreign ministry spokesman referred to them as “thoughtless and irresponsible.” The Tehran Times quoted the spokesman as saying that “the US is retrogressing and repeating the mistakes of the previous administration.”

In another indication of the military pressure that Washington is bringing to bear on Iran, President Obama has ordered a carrier strike group, led by the aircraft carrier USS Eisenhower, into the Persian Gulf for a six-month deployment. The flotilla, including 6,000 sailors and Marines, four squadrons of fighter bombers and several missile cruisers and destroyers, set sail for the region on January 2.

The military escalation is running parallel to the Obama administration’s attempt to punish Iran with a new set of economic sanctions. The so-called P5+1—the US, France, Britain, Russia, China and Germany—is set to meet in New York City Saturday to discuss punitive measures against Iran, over and above three earlier rounds of sanctions imposed by the United Nations Security Council over Iran’s refusal to suspend its uranium enrichment program.

The six powers had imposed an end-of-the-year deadline on Tehran to accede to a proposal made by the International Atomic Energy Agency, the UN nuclear watchdog, that would have compelled Iran to ship most of its low-enriched uranium (LEU) to Russia and France to be refined into reactor fuel.

Tehran ignored the deadline and put forward its own counter-proposal to exchange batches of the LEU for nuclear reactor fuel from Turkey, with which Iran has been developing close economic ties. The US and the other Western powers have ignored this proposal.

Secretary of State Hillary Clinton said this week that Washington wants the implementation of “smarter sanctions” that would target “decision-makers.” Media reports have indicated that the US is pushing for a wide range of new sanctions against the Islamic Revolutionary Guard Corps, which is involved in Iran’s nuclear program, but also controls broad swathes of the Iranian economy, ranging from the Tehran airport to national telecommunications, with substantial investments in thousands of enterprises.

It is highly unlikely, however, that any substantial new round of sanctions will gain the approval of the UN Security Council, which is chaired by Beijing this month. Both Russia and China are among the five countries with veto power and neither has any interest in halting economic relations with Iran.

China is rapidly expanding trade with Iran and investment in its energy sector. Iran is now the third-largest supplier of crude oil to China and also exports large amounts of natural gas. For its part, Russia is responsible for 85 percent of Iran’s weapons imports. Both countries have interests in the region that are in conflict with those of Washington and do not see the Iranian nuclear program as any real threat.

Nor for that matter is the threat of an Iranian bomb the driving force behind US policy. US imperialism is seeking to establish its hegemony over the energy-rich regions of Central Asia and the Middle East, where it is now waging two wars—in Iraq and Afghanistan, with Iran lying between the two. It is seeking to reassert US dominance in Iran at the expense of its geo-strategic rivals and is threatening to ignite a conflict that could trigger a far wider war with incalculable consequences.

In the absence of Security Council approval, Washington will likely impose its own unilateral sanctions, with the support of Britain and other allies. Legislation now pending in the US Congress would give the Obama administration the power to enforce an embargo on Iran’s importation of refined petroleum. With Iran dependent on imports for 40 percent of its refined petroleum, such a measure would have a crippling effect and would be tantamount to the launching of a war.

Obama was elected in 2008 promising a new policy of “engagement” with Iran. As he nears the end of his first year in office, however, Washington’s rhetoric and policies are turning more and more threatening, while the diplomatic actions over Iranian sanctions begin to resemble the maneuvers staged by the Bush administration over Iraqi “weapons of mass destruction” in the run-up to the Iraq war.