US senators proposed further tightening sanctions on Iran reflecting fears that companies overseas, particularly in China, are evading U.S. penalties imposed last year for doing business with Iran, Reuters reported on Wednesday.

The bipartisan group said they wanted to increase pressure on Tehran in order to stop its suspected pursuit of nuclear weapons, pointed out in the data this week from the U.N. nuclear watchdog.

The International Atomic Energy Agency revealed in a report that Iran has tried to weaponize its nuclear program. However, Iran says that its Uranium enrichment program is for generating peaceful nuclear energy, but the west suspects it is aimed at making a bomb.

The bill was introduced a day after seven foreign firms including Venezuela's state-owned oil company were penalized for trading with Iran.

Congress should pass, and the administration should robustly enforce, strengthened sanctions against Iran to ensure that every effort is made to prevent Iran from threatening the United States and our allies in the region with nuclear weapons, said Senator Susan Collins, a Republican co-sponsor of the bill, reported Reuters.

The legislation with its similarity to a measure under consideration in the House of Representatives has made it more probable that some tightening of sanctions will pass in the current session of Congress ending in 2013. Also targeted are the governments of North Korea and Syria with the new sanctions.

The U.S. sanctions law, passed last year, tried to pressure Iran to drop its nuclear work by targeting its energy and banking sectors. The new bill would strengthen that law by exposing joint business ventures with Iranian energy entities to sanctions, the senators said.

it is required for the State Department to pass the requests from the lawmakers. Once the bill is passed, it would penalize any company that sells goods for military applications to Iran, North Korea or Syria, by freezing assets and denying access to the U.S. banking system.

The Venezuelan state oil company PDVSA was charged with sanctions for supplying a gasoline blending component to Iran on Tuesday. Other companies sanctioned were from the United Arab Emirates, Singapore, Israel and Monaco.