Washington — Rob Malley, the U.S. special envoy for Iran, has been on leave while his security clearance is under review. 

"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," Malley said in a statement to CBS News. "In the meantime, I am on leave."

State Department spokesman Matthew Miller confirmed that Malley was on leave and told reporters Thursday, "Abram Paley is serving as acting special envoy for Iran and leading the department's work in this area."

In President Barack Obama's administration, Malley had a hand in everything from the Iran nuclear deal negotiations to the fight against the Islamic State. Under the 2015 nuclear agreement, Iran curtailed its nuclear program in order to receive sanctions relief. After President Donald Trump's withdrawal from the deal, Malley has played a central role in trying to revive it under President Joe Biden. 

Malley's absence coincides with multiple reports in recent weeks that the U.S. has restarted indirect talks with Iran on the nuclear and detainee issue. National Security Council Middle East Coordinator Brett McGurk has also recently played a role.

This week, Secretary of State Antony Blinken said at an event at the Council on Foreign Relations there was "no agreement in the offing" and any reports of a deal being reached were misleading.

Malley has also been involved in negotiations to secure the release of Americans who the U.S. says are wrongfully detained in Iran. 

In a letter Friday, House Foreign Affairs Committee Chairman Michael McCaul wrote to Blinken to raise a number of concerns surrounding Malley's leave. He quoted a CNN report that said that "Malley's clearance was suspended amid a State Department diplomatic security investigation into the possible mishandling of classified information." CBS News has not confirmed that this is the case. 

McCaul also questioned Blinken over what he said was the State Department's "lack of responsiveness" concerning oversight of the administration's negotiations with Iran. He said his committee has "repeatedly" asked for Malley's testimony, but the State Department hasn't granted this request.

The chairman said that his committee had been told by the State Department that Malley could not appear before Congress because his leave since some time in May was "due to the illness of a close family member." He said no one at the department ever indicated that Malley's clearance had been suspended or was under review for any reason.

In:
• Iran
• Iran Nuclear Deal

Margaret Brennan

Margaret Brennan is moderator of CBS News' "Face The Nation" and CBS News' senior foreign affairs correspondent based in Washington, D.C.