A significant Republican in the U.S. House of Representatives has requested information from Secretary of State Antony Blinken regarding a probe of the U.S. ambassador for Iran’s security clearance after allegations that he may have improperly handled secret materials.

Michael McCaul, the chair of the Foreign Affairs Committee, wrote to Blinken on Friday inquiring as to why Rob Malley, the State Department’s special representative for Iran, had been placed on unpaid leave following the suspension of his security clearance earlier this year to look into the alleged improper handling of classified documents.

The committee had previously asked Malley to testify in an oversight hearing about the State Department’s negotiations with Iran but said the department responded that Malley could not testify due to the illness of a close family member.

“Given the gravity of the situation, it is imperative that the Department expeditiously provide a full and transparent accounting of the circumstances surrounding Special Envoy Malley’s clearance suspension and investigation and the Department’s statements to Congress regarding Special Envoy Malley,” McCaul wrote Blinken in a letter posted on the panel’s website.

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

On Thursday, Malley told Reuters: “I have been informed that my security clearance is under review. I have not been provided any further information, but I expect the investigation to be resolved favorably and soon. In the meantime, I am on leave.”

Asked to comment on McCaul’s letter, Malley on Saturday said he stood by Thursday’s statement, adding, “I am eager to know what the State Department’s review is about and, as I have made clear from the outset, am prepared to cooperate fully with it.”

Appointed soon after Democratic President Joe Biden took office in 2021, Malley had the task of trying to revive the 2015 Iran nuclear deal. Then-President Donald Trump’s abandoned the pact in 2018 and reimposed U.S. sanctions on Tehran.

Having failed to revive the deal, the United States has held talks with Iran to try to ease tensions by sketching out steps that could limit the Iranian nuclear program, release some detained U.S. citizens and unfreeze some Iranian assets abroad, Iranian and Western officials said earlier this month.

In the letter, McCaul asked that Acting Special Envoy for Iran Abram Paley and National Security Council Coordinator for the Middle East and North Africa Brett McGurk be made available to testify and provide classified briefings to the Committee by the end of July.