Russian Foreign Minister Sergei Lavrov and his US counterpart John Kerry called on Wednesday for an agreement on a nuclear deal with Iran to be reached as soon as possible.

"The need to reach as soon as possible a comprehensive agreement which would allow to fully normalise the situation around the Iranian nuclear programme has been acknowledged," the Russian foreign ministry said following a call between Lavrov and Kerry.

They spoke after Iran and world powers met in Oman on Tuesday amid signs that an elusive deal on Tehran's nuclear programme might not be struck by a November 24 deadline.

Russia's chief negotiator Sergei Ryabkov said after Tuesday's talks that he was still "reasonably optimistic".

The agreement is aimed at easing Western suspicions over Tehran's nuclear intentions as well as damaging sanctions on the Iranian economy.

On Tuesday, Russia signed a contract to build two nuclear reactors at the existing Russian-built Bushehr plant and announced plans for a total of nine.

State Department spokeswoman Jen Psaki confirmed the two men had spoken about the Iran negotiations by phone on Wednesday, but did not go into detail about their conversation.

She said however that Russia's contract with Iran was "technically separate from the negotiations over a nuclear deal".

"Broadly speaking, civilian nuclear cooperation is not prohibited by UN Security Council resolutions," Psaki told reporters.

US senators: Iran deal must dismantle nuclear program
Washington (AFP) Nov 12, 2014 - Two US senators responsible for introducing strict sanctions on Iran renewed their warning Wednesday over nuclear negotiations with the country, saying any final pact must "dismantle" the Islamic republic's nuclear program.

Their remarks follow three days of nuclear talks in Oman between Iran and the P5+1 -- UN Security Council permanent members Britain, China, France, Russia and the United States, plus Germany -- with a November 24 deadline looming to strike a comprehensive agreement.

"We believe that a good deal will dismantle, not just stall, Iran's illicit nuclear program and prevent Iran from ever becoming a threshold nuclear weapons state," Senate Foreign Relations Committee chairman Robert Menendez and Republican Senator Mark Kirk said in a statement.

Should a potential deal fail to achieve such goals, including a robust inspection and verification regime and strict limits on nuclear-related research, "we will work with our colleagues in Congress to act decisively, as we have in the past."

Menendez and Kirk have worked since 2011 to draft and pass multifaceted economic sanctions against Tehran, and their statement was aimed at pressing international negotiators for a strong deal that would keep Iran's feet to the fire on its nuclear program.

"Gradual sanctions relaxation would only occur if Iran strictly complied with all parts of the agreement," the lawmakers said.

Their most recent bill, which would impose new measures should the negotiations fail, has been blocked since the end of 2013 by President Barack Obama's Democratic allies in the Senate.

His administration had wanted the negotiations to proceed without interference from Congress.

But Republicans, who snatched the Senate majority from Democrats in last week's midterm elections and take control when the next congressional session convenes on January 3, may not show the same deference.

"I want a vote on sanctions in case the deal falls apart," Senate Republican Lindsey Graham told reporters on the first day back after a seven-week recess.

"This is the most important foreign policy issue that any president will decide in generations."

Faced with the prospect of unilateral action by the US Congress, Iranian President Hassan Rouhani said that "each country must resolve its own problems," although he did not name the United States.

Final nuclear talks between the P5+1 and Iran are set for November 18 in Vienna.