President Barack Obama said on Wednesday his administration would have to make tough decisions soon on the wars in Iraq and Afghanistan, after convening his first meeting of U.S. military chiefs.

"We are going to have some difficult decisions that we are going to have to make surrounding Iraq and Afghanistan most immediately," Obama told reporters after his first session with the Joint Chiefs of Staff since taking office eight days ago.

Obama has pledged to build up U.S. troop levels in Afghanistan while working toward an accelerated withdrawal of forces in Iraq, a war that polls show most Americans oppose.

"Obviously, our efforts to continue to go after extremists who would do harm to the homeland is uppermost on our minds," Obama said, signaling his strategy of focusing more on Afghanistan, a departure from the Bush administration's emphasis on Iraq.

Obama's first presidential visit to the Pentagon to confer with top generals was intended to build upon a White House meeting with U.S. commanders on Iraq and Afghanistan last Wednesday, his first full day in office.

But his Defense Department visit was low key compared to his high-profile appearance at the State Department last week soon after he was sworn in, a possible signal of his intention to stress diplomacy over military power in world affairs.

Pulling troops out of Iraq was a cornerstone of Obama's campaign for the presidency, during which the war was a top concern of voters until it was eclipsed by the faltering economy.

Obama said before taking office that he wanted U.S. combat forces out of Iraq within 16 months of starting his term. His ability to make good on that promise could hinge on whether violence in Iraq keeps declining and Iraqi security forces keep improving their capabilities.