At his confirmation hearing before the Senate Armed Services Committee, Mullen, who would replace Gen. Peter Pace, said such a withdrawal would have an impact on the stability of the entire region.
Mullen admitted a U.S. military presence cannot solve Iraq's problems. A solution, he said, must come from the Iraqi government, which has failed to adopt legislation necessary to bring about national reconciliation.
"I worry a lot about moves which would turn Iraq into a cauldron and I think that would not be just bad for the people of Iraq, not just bad for the people of America, but for our vital interests in that part of the world," Mullen said.
Mullen said he backs continued debate on Capitol Hill over the course of the war.
"I think we need to bring as much pressure on them as we possibly can," Mullen said.