Iran Will Not Be Duped in Nuclear Deal: Ayatollah Ali Khamenei

Iran's negotiating team will not be duped in any nuclear deal with world powers, the country's supreme leader, Ayatollah Ali Khamenei, said Thursday.

Referring to a letter sent to Iran by Republican senators in the United States, Khamenei said it indicated "the extreme decadence of political ethics and the collapse of the American system from within," ISNA news agency reported.

Speaking before the Assembly of Experts, Iran's highest clerical body, he praised Iran's "trustworthy" team negotiating with the "deceitful" world powers.

President Hassan Rouhani "has selected a nuclear (negotiating) team who are truly good, trustworthy and hardworking," he said, whereas "the other party is deceitful and stabs in the back".

Iranian officials "know what they are doing and they also know how to act in case of an agreement so that Americans cannot break it later", said Khamenei, who has Tehran's final say on any deal.

"The Americans and their allies always adopt a tougher, sharper and louder tone when deadlines are looming in order to achieve their objectives, but it is a trick," said Khamenei.

In the letter, criticised in the Islamic republic and by the US administration, senators stressed that President Barack Obama will leave office in January 2017 and that his successor could scrap any nuclear deal if Congress has not approved it.

On Tuesday, Iranian Foreign Minister Mohammad Javad Zarif told the Assembly of Experts the letter had sapped Tehran's confidence in dealing with the United States.

The letter appeared to be another bid to influence or even derail the talks between Iran and the P5+1 powers - which include Britain, China, France, Germany and Russia as well as the United States.

With a March deadline looming, negotiators are furiously working to agree the political outlines of a deal that would curb Iran's nuclear programme in return for a lifting of Western sanctions.

A new round of talks between Zarif and US Secretary of State John Kerry is due to take place in Lausanne, Switzerland on Sunday.