President Obama said there were difficult days ahead
US Republicans have broadly welcomed President Barack Obama's plan to withdraw most troops from Iraq by 2010.
However, they suggested he should give credit to his predecessor for stability brought by the "surge" strategy of pouring extra troops into Iraq.
House Republican Minority Leader John Boehner described the plan as responsible while remaining flexible.
Iraqi PM Nouri al-Maliki said his forces were capable of controlling security in Iraq after US troops leave.
President Obama announced that the US "combat mission" would officially end by August 2010.
However, up to 50,000 of 142,000 troops now there will stay until the end of 2011 to advise Iraqi forces and protect US interests, he said.
Mr Obama praised the progress on security made but warned: "Iraq is not yet secure, and there will be difficult days ahead."
A London-based spokesman for Mr Maliki's party, Zuhair al-Nahar, told the BBC: "The Iraqi security forces have proved their efficiency and have proved their capability.
"In many provinces, for example in the south, you hardly see any presence of American troops and in many areas of Baghdad the same applies.
"So the Iraqi security forces have shown that they are capable of controlling the security situation."
Among Republican support, House Republican Minority Leader John Boehner said Mr Obama had outlined "a responsible approach that retains the flexibility to reconsider troop levels and to respond to changes in the security environment".
Republican Senator John McCain, Mr Obama's former rival presidential candidate, said he supported the plan.
He said it was "one that can keep us on the right path in Iraq," the Associated Press news agency reported.
He told senators: "Let us have no crisis of confidence now.
"Instead, let us welcome home our fighting men and women - not just thanking them for serving in Iraq, but congratulating them on bringing us to victory there."
However, Democratic congressman Dennis Kucinich questioned keeping some troops in Iraq while withdrawing others.
"You can't be in and out at the same time," he said.
Some Democrats are concerned that the timetable falls short of Mr Obama's election pledges on troop withdrawal.
Mr Obama had said previously that he would completely pull out troops within 16 months of taking the top job in January 2009.
In his address at Camp Lejeune, a Marine Corps base in North Carolina, Mr Obama said his national security team had drawn up a "new strategy" for US involvement in Iraq.
The strategy recognised that the long-term solution in Iraq must be political and that the most important decisions about its future must now be made by Iraqis, he said.
Senate Majority Leader Harry Reid described Mr Obama's plan as "sound and measured" but said the US "must keep in Iraq only those forces necessary for the security of our remaining troops and the Iraqi people".
House Speaker Nancy Pelosi said the plan was "good news" because it signalled an end to the war, but called for clearly-defined missions for the remaining troops.
REACTION TO BARACK OBAMA'S IRAQ PLAN
President Obama very appropriately and correctly thanked US Marines for precipitating the turnabout in Iraq. But if there is a chance of success in Iraq now as defined by Barack Obama, shouldn't there be some mention of the change in strategy, and the former Commander in Chief, the guy who hung in there?
Several Democratic leaders have voiced strong concerns about the size of the "transition force." What's more, for all of the success in reducing violence in Iraq, long-term political progress remains elusive, and will have to be a high priority for the administration. Still, Obama has outlined the beginning of the end. It's about time.
In 2003, then Maj Gen David Petraeus, commander of the 101st Airborne Division that had participated in the invasion of Iraq, had a running joke with an embedded reporter... The general would turn to the reporter and muse, "Tell me how this ends." Today at Camp Lejeune... President Barack Obama - an antiwar Illinois state senator at the time of the invasion - answered Petraeus.
2011 just became a hard stop, I think. When presidents lay down markers like that, they don't easily walk away from them. It's now what Iraqi politicians described it as: the American Withdrawal of Forces Agreement. I fear Iraqi domestic political convenience just became American strategic reality. This converts the SOFA from a framework for a long-term strategic partnership to a guarantee of withdrawal.
The Weekly Standard