Khamenei blasts Republican letter, calls US 'backstabbing'

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

After the fallout from an open letter sent to Iran by Republican senators, Khamenei appeared before the Assembly of Experts, Iran's highest clerical body, to praise 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, quoted by ISNA news agency, 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 the final say on any deal.

In the five paragraph letter, which has drawn criticism from both the Islamic republic and the US administration, senators stressed that President Barack Obama is in office only until January 2017.

"We will consider any agreement regarding your nuclear-weapons program that is not approved by the Congress as nothing more than an executive agreement between President Obama and Ayatollah Khamenei," the letter said. "The next president could revoke such an executive agreement with the stroke of a pen."

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

A day before, Zarif released his own letter in response to the Republicans, saying he found it "very interesting" that "some political pressure groups are so afraid even of the prospect of an agreement that they resort to unconventional methods, unprecedented in diplomatic history."

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

With a March deadline looming, negotiators are furiously working to agree on 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.