U.S. Navy Admiral Michael Mullen will be sworn in Monday as the chairman of the Joint Chiefs of Staff.

Admiral Mullen, former chief of naval operations, replaces Marine General Peter Pace as the nation's top military officer.

He will serve as the senior military advisor to both President Bush and Defense Secretary Robert Gates.

During his confirmation hearings in August, Admiral Mullen told the Senate Armed Services Committee the deployment of additional U.S. troops to Iraq has made the security situation better, but "not great," and that political reconciliation was the only solution.

Mullen also expressed concerns over Iran's "increasingly hostile" role in the Middle East.

Gates announced earlier this year that Pace would not seek a second term as Joint Chiefs chairman. The defense secretary said the decision was not made based on performance, but rather that the unpopularity of the Iraq war would make reconfirmation hearings difficult.

Some information for this report was provided by AFP and AP.