Amid threats from both sides, North Korea yesterday cut the phone “hotline” between the two Koreas and abrogated the 1953 armistice that ended the Korean War. The move came as American and South Korean troops began joint military exercises and Washington announced new sanctions against Pyongyang.

The escalation of tensions on the Korean peninsula follows last week’s UN Security Council resolution imposing further punitive measures on North Korea over its third nuclear test on February 12. As well as previous UN sanctions, the North Korean regime has also been subject to a US-led economic and diplomatic blockade since the end of the Korean War.

An editorial in North Korea’s state-run Rodong Sinmun yesterday declared that “the armistice agreement has been nullified” and warned “no one can expect what will happen next.” The 1953 armistice stopped the fighting but did not formally end the war. Pyongyang has pressed for decades for a formal peace treaty with the US, only to be repeatedly rejected.

North Korea has previously declared the armistice void, most recently in 2009 in response to a previous round of sanctions that the US pushed through the UN. Tensions flared in 2010 following the sinking of the South Korean corvette, the Cheonan, for which North Korea denied responsibility. Amid provocative US-South Korean naval exercises, the two Koreas engaged in artillery exchanges in which several South Korean soldiers and civilians on Yeonpyeong Island were killed.

On Sunday, North Korean leader Kim Jong-un visited an artillery unit that took part in the 2010 shelling, urging it to “deal deadly counterblows to the enemy if a single shell is fired on the waters.”

Exercise Key Resolve, involving 10,000 South Korean troops and more than 3,000 American military personnel, began yesterday and will continue until March 21. During the war games, the Pentagon has supplemented the 28,500 US troops stationed in South Korea with additional personnel, as well as extra warships and warplanes.

No military incidents or clashes involving the two Koreas have been reported to date. Moreover, several dozen South Korean managers continued their daily trip yesterday to the Kaesong industrial zone inside North Korea, where they supervise some 50,000 workers making goods for South Korean businesses.

Both sides, however, have engaged in bellicose rhetoric. Last week, as the UN Security Council prepared to impose further sanctions, Pyongyang warned that it would “exercise the right to a pre-emptive nuclear attack” to defend the country and claimed to have the ability to carry out a precision attack on Washington.

South Korea’s defence ministry warned last Friday that the North’s government would “evaporate from the face of the Earth” if it ever used a nuclear weapon. Newly-elected South Korean President Park Geun-hye told her first cabinet meeting yesterday: “We must deal strongly with a North Korean provocation.”

Kim Byung-kwan, Park’s appointee as defence minister, declared during his confirmation hearing that South Korea would respond to a North Korean artillery attack by destroying the regime. Kim, who was former deputy commander of the joint US-South Korean forces, is known to carry a photo of the president’s father—former South Korean military dictator Park Chung-hee—who ruled from 1961 to 1979.

The most chilling threat came from Washington. Obama’s National Security Adviser Tom Donilon yesterday warned: “There should be no doubt: we will draw upon the full range of our capacities to protect against, and to respond to, the threat posed to us and to our allies by North Korea.” The “full range” obviously includes the huge American nuclear arsenal. Donolon added that Washington would hold Pyongyang “full accountable” for any transfer of nuclear weapons or materials to other countries.

The US Treasury announced more penalties against North Korea yesterday, targeting the country’s main foreign exchange bank—the Foreign Trade Bank—and a senior official, Paek Se-bong, who is allegedly connected to North Korea’s missile program. The US State Department also designated another three individuals for sanctions.

The Obama administration is directly responsible for the rising tensions in North East Asia. Its “pivot to Asia” aimed at undermining China has encouraged governments throughout the region, including South Korea, to take a more aggressive stance. By putting the pressure on China’s ally North Korea, the US is also compounding the problems facing Beijing.

China has continued to economically prop up North Korea to prevent a political implosion and the possibility of a pro-US regime on its northern border. At the same time, Beijing has voted for UN sanctions and sought to rein in North Korea, fearing that Pyongyang’s nuclear tests could provide South Korea and Japan with a pretext for developing their own nuclear weapons.

South Korean lawmaker Chung Mong-joon, from Park’s right-wing Saenuri party, has already suggested that the country should build a “nuclear deterrence”. He told a meeting of the party’s National Assembly members last month that the current situation was like trying to defend oneself with a pebble against a gangster with a machine gun. The JoongAng Ilbo described North Korea’s nuclear test as an existential threat and argued that South Korea should develop its own nuclear weapons, rather than rely on the US.

Such comments only add to the pressure in Beijing, where a debate has opened up in ruling circles over China’s alliance with North Korea. While there has been no shift in China’s official stance, senior officials and academics have advocated a tougher line against Pyongyang, including ending the security treaty between the two countries.

At the same time, Beijing is well aware that the US is encouraging North Korea to adopt a more pro-Western orientation. US National Security Adviser Donilon yesterday referred to the transformation of US relations with Burma, saying it had resulted in billions of dollars in Western aid, investment and debt forgiveness. It was a not-so-subtle hint that Pyongyang could make the transition from pariah to “democracy” if it toed Washington’s line.

The US has, however, flatly refused to make any concessions to North Korea unless it dismantles its missile and nuclear programs. Pyongyang agreed to do so in the past—under the 1994 Agreed Framework and the 2005 agreement reached at six-party talks—only to be confronted with broken promises and new demands from Washington.

The aggressive US stance ensures that the Korean peninsula remains extremely tense, heightening the danger of conflict in one of Asia’s critical flashpoints.