U.S. Ambassador to Iraq Zalmay Khalilzad will be nominated to replace John Bolton as U.S. Ambassador to the United Nations, a senior administration official confirmed to FOX News on Thursday.

The timing of the announcement has not been set, but rumors about Khalilzad have been floating since Bolton announced last month that he would submit his resignation and leave the world body when his temporary appointment expired at the end of the last Congress.

A separate State Department official also told FOX News that he had heard from "a pretty reliable source" on Secretary of State Condoleezza Rice's staff that Khalilzad would be tapped for the job as top U.S. diplomat.

"This building's not too happy," the source said. "No one here likes Zal. He is known as being a pain in the ass to work for and doesn't get on well with the Foreign Service."

A separate source in Foggy Bottom who did not confirm the nomination said Khalilzad had been passed over for the job of deputy secretary of state "because he's known as a lousy manager."

Reports surfaced Wednesday evening that Director of National Intelligence John Negroponte would step down from his post to take the State Department position. Khalilzad took the job in Iraq from Negroponte after he was tapped to be DNI two years ago.

A former administration official said Khalilzad "wants [the U.N. job] very, very badly. It gets him out of [Iraq] and he thinks it will make him a bigger player in the administration."

The White House had been tight-lipped about any other possible candidates for the post. Other names that had been floated in Washington included Deputy Amb. Alejandro Wolff and Under Secretary of State for Political Affairs Nicholas Burns.

For months, the Bush administration had been searching for some way to keep Bolton in the post at the United Nations but gave up on getting any sort of straight-up confirmation after Bolton had been unable to win support from Democrats on the Senate Foreign Relations Committee.

Administration officials had thought Bolton could get confirmed if his nomination could get to the floor, but going around the committee process would have created too much collateral political damage in the new Congress and was ruled out.

Senate Foreign Relations Committee aides say members were informed of the president's intent to nominate Khalilzad, and he is pretty popular on Capitol Hill. Several aides on both sides of the aisle told FOX News they expect smooth-sailing for the nominee quite, a welcome departure from the tumultous Bolton hearings.

FOX News' Bret Baier, James Rosen and Trish Turner contributed to this report.