Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif
Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad ZarifReuters

American Senator Bob Corker claimed on Tuesday that five of the six world powers negotiating with Iran over its nuclear program have stepped back, leaving Washington to hammer out a deal with Tehran, reports AFP.

"It's evident that these negotiations are really not P5+1 negotiations anymore," Corker, who heads the Senate Foreign Relations Committee, said as he emerged from a closed-door briefing by Obama administration officials on the status of nuclear talks with Iran.

"It's really more of a bilateral negotiation between the United States and Iran," he added.

The P5+1 are the five permanent UN Security Council members (Britain, China, France, Russia and the United States) plus Germany. They have undertaken years-long talks with Iran in a bid to halt the Islamic republic's nuclear drive.

Several rounds of sanctions have been imposed on Iran, cutting deeply into the country's economy.

The sides powers reached an interim deal in November of 2013, under which Iran committed to limit its uranium enrichment to five percent and is gradually winning access to $4.2 billion of its oil revenues frozen abroad and some other sanctions relief.

The sides were then supposed to continue talks and turn the interim deal into a permanent. However, the talks have stalled and two deadlines for a final deal have been missed, with a third one now looming.

President Barack Obama met with German Chancellor Angela Merkel at the White House on Monday, and Obama said he saw no reason to further extend the current deadlines.

The present issue, Obama said, was "does Iran have the political will and the desire to get a deal done?"

With an end-March deadline for a political agreement approaching, and a final deal confirming technical details required by June 30, Corker said the key players are now essentially Washington and Tehran.

"I was in Munich this weekend (for an international security conference) and was very aware that this was becoming more of a one-on-one negotiation," the Senate Republican told reporters, according to AFP.

Corker and the Democrat he replaced as committee chairman, Senator Robert Menendez, left the latest briefing expressing concern about the administration basing negotiations on the need to maintain Iran's potential nuclear weapons "breakout" time to at least one year.

"One of my major concerns all along that is becoming more crystal clear to me, is that we are, instead of preventing proliferation, we are managing proliferation," Menendez was quoted as having said.

Having Iran just one year away from building a bomb would be "a different world and a far more challenging world," he added.

Recent reports indicated that the United States is ceding ground to Iran in talks and will now allow it to “keep much of its uranium-enriching technology,” thus allowing Iran to maintain its self-proclaimed “right to enrich uranium”.

Lawmakers in Washington, concerned about an agreement with Iran that would allow it to advance its nuclear program, have been calling for more sanctions against Iran, even as talks are ongoing.

A bill introduced last year by Menendez and Senator Robert Kirk was gaining momentum in Congress, but Obama lobbied hard against it and has more than once threatened to veto the bill if it passes.

The Banking Committee recently voted 18-4 in favor of advancing the bill that would toughen sanctions on Iran if international negotiators fail to reach an agreement on its nuclear program by the end of June.

However, the bill is not expected to come up for a vote in the full Senate until at least March 24.