US senators have vowed to stay the implementation of new Iran sanctions if Tehran takes verifiable steps such as immediately halting uranium enrichment, ahead of a new round of talks on its suspect nuclear program.

In a letter sent to President Barack Obama last week, a group of leading Democratic and Republican senators said they would be prepared to match Iran's actions and hold off threatened new sanctions on the already struggling Iranian economy.

"Iran's first confidence-building action should be full cooperation with the International Atomic Energy Agency," the group, led by the Democratic chairman of the Senate Foreign Relations committee, Senator Bob Menendez.

Tehran should also implement all UN Security Council resolutions on its nuclear weapons program "to include immediate suspension of all enrichment activity."

"If the Iranian government takes these steps in a verifiable and transparent manner, we are willing to match Iran's good-faith actions by suspending the implementation of the next round of sanctions currently under consideration by the Congress," said the letter released on Monday.

"In short, the US should consider, with the other members of the P5+1, a 'suspension for suspension' initial agreement -- in which Iran suspends enrichment and the US suspends the implementation of new sanctions," it added.

"Such an agreement would ease concerns that Iran is using the talks as a subterfuge while its centrifuges spin and for Iran it would suspend critical additional sanctions on its key economic sectors."

The letter, signed by 10 US senators, including veteran Republicans John McCain and Lindsey Graham, stressed however that in the meantime the threat of military force remained and called on Obama to up the pressure on Iran through existing sanctions.

Iran will meet on Tuesday in Geneva with the members of the P5+1 -- Britain, China, France, the United States and Russia as well as Germany -- for the first nuclear talks since Iranian President Hassan Rouhani took office in August.

Following overtures fom Iranian officials, including Rouhani, at the UN General Assembly in September, hopes are high that Iran may bring a new substantive offer to the table.

Draft legislation for new American sanctions targeting the automobile sector and Iran's foreign reserves was adopted in July by the House of Representatives, and had been due to come to the Senate for a vote in the fall.

The Islamic Republic's economy has been severely damaged by four rounds of UN sanctions, as well as separate US and EU sanctions, aimed at reining in the atomic program, particularly the enrichment of uranium which can be used in a nuclear warhead.

The West has long accused Iran of seeking to develop a nuclear bomb under the guise of its nuclear energy program, which Tehran says is for civilian purposes only.