Efforts to approve tougher sanctions against Iran in the last days before Congress ends its term have fallen through due to partisan disagreements and political disputes.
Republicans blocked the bill - composed of two pieces of legislation which had passed in the House of Representatives - from reaching the Senate floor.
The first section was meant to close loopholes in the existing legislation and prohibit ties between US firms and international companies doing business with Iran's energy sector. The second, originally introduced by Senator Barack Obama, the Democratic presidential candidate, would provide legal backing to those divesting from companies doing business with Iran.
This has put an end to chances the bill will pass in this congress, which will probably not re-convene until the new congress is sworn in. Democrats had argued that the reason behind the rejection was that Mr Obama's name was attached to one of its parts and Republicans feared it would help him bolster his standing on foreign-policy issues, a claim rejected by Republicans.
In the House of Representatives, legislation calling for increased inspections on shipments to and from Iran was not taken to the floor for a vote. Liberal groups argued it effectively called for a blockade against Iran, which might lead to war, and Democratic leaders decided not to vote on it until a new version is introduced.
All these suggested measures were strongly supported by the pro-Israel lobby, which is advocating strengthening the pressure on Iran.