WASHINGTON - US Senate Republicans blocked new economic sanctions on Iran's oil sector on Thursday, saying they needed more time to study revisions, a surprise move that drew anger from Senate Democrats who had expected unanimous approval ahead of Iran talks on May 23.

"I feel I've been jerked around," Democratic Leader Harry Reid said on the Senate floor after the Republican objection.

But Senate Republican Leader Mitch McConnell said his staff did not receive a draft of the bill until late on Wednesday night, and needed more time to make sure it was as strong as possible.

"There is no reason in the world why we can't resolve whatever differences we have and move forward," McConnell said. "We certainly don't want to take a step backward, and there are members on my side of the aisle who are concerned that the way the measure is currently crafted could actually be a step in the wrong direction," McConnell said.

The United States says Iran's nuclear program is a cover for developing the capability to build atomic bombs, while Iran says it is for civilian purposes.

The sanctions are meant to shut down any financial deals with Iran's powerful state oil and tanker enterprises, stripping Tehran of crucial oil revenues. The new bill would build on penalties signed into law by President Barack Obama in December that threatened sanctions against any foreign institutions trading with Iran's central bank.

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Democrats wanted to pass the proposed penalties ahead of talks between world powers and Iran next week, and had support from the American Israel Public Affairs Committee, a powerful pro-Israel lobby group.

But Republicans sought a stronger statement in the bill that the use of US military force was an option.

"These sanctions are great. I hope they will change Iranian behavior. They haven't yet, and I don't think they ever will," said Senator Lindsey Graham of South Carolina.

"I want more on the table," Graham said.

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