WASHINGTON — The United States should immediately impose sanctions on Russia and China under a US law that punishes major investments in Iran’s energy sector, a senior US lawmaker said Monday.

“It’s time to implement our sanctions laws and demonstrate to Russia and China that there are consequences for abetting Tehran and flouting US sanctions,” Representative Ileana Ros-Lehtinen said in a statement.

Ros-Lehtinen, the top Republican on the House Foreign Affairs Committee, said firms run by the Russian and Chinese governments had invested “huge sums” in Iran’s energy sector, “effectively bankrolling” Tehran’s alleged nuclear weapons program and its backing of Islamist groups.

She did not offer details, but US officials have noted that Chinese firms have been stepping in to fill the void left by companies leaving Iran because of UN and US sanctions.

“Russia and China appear determined to continue to facilitate Iran’s dangerous policies. This must not be allowed to continue without serious repercussions,” she said.

Her comments came as a top US State Department official, Robert Einhorn, was on a trip to Asia set to include a stop in Beijing to press China to fully enforce sanctions on Iran.

China has invested around 40 billion dollars in the Islamic republic’s oil and gas sector, but Chinese imports of Iranian oil fell in the first half of 2010, a senior Iranian official told Mehr news agency on Saturday.

In 2009, China became Iran’s premier trading partner, with bilateral trade worth 21.2 billion dollars against 14.4 billion dollars three years earlier.