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 letter, which has drawn criticism in both the Islamic republic and from the US administration, senators stressed that President Barack Obama is in office only until January 2017 and a 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 that the letter had sapped Tehran's confidence in dealings with the United States.
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 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.