US media reports indicated that Republican Michael McCaul had sent a letter to Blinken - on Tuesday, Friday - asking him about the reason for granting unpaid leave to the US State Department's special envoy for Iran after he suspended his security clearance earlier this year to investigate allegations of Not true in classified documents.

The committee previously asked the envoy to testify at a hearing on the US State Department's negotiations with Iran, but said that the ministry replied that Malley could not testify due to the illness of a close family member.

"Given the seriousness of the situation, it is imperative that the State Department urgently provide a full and transparent explanation of the circumstances surrounding the suspension of Special Envoy Malley, as well as the department's investigations and statements to Congress concerning the Special Envoy," McCool wrote in his letter, which was published on the committee's website.

The US State Department did not immediately respond to a request for comment on the letter.

Malley, for his part, told Reuters last Thursday, "I was informed that my security clearance is under review. I have not received any other information, but I expect that the investigation will end with a good result soon. Right now, I am on leave."

In response to a request to comment on McCall's letter, Malley said: "I am eager to know what the Foreign Ministry's investigation is about, and of course I am ready to cooperate fully in this matter."

Malley was appointed shortly after President Joe Biden took office in 2021, and was tasked with trying to revive the 2015 Iran nuclear deal after former President Donald Trump's decision in 2018 to withdraw from the deal and reimpose US sanctions on Tehran .

Malley contributed to the drafting of the nuclear agreement in 2015, and played a central role in former President Bill Clinton's attempt in 2000 to mediate a peace agreement between Israel and the Palestinians, an attempt that failed.