Washington  - US President Barack Obama announced Tuesday that he has ordered the deployment of more than 15,000 additional troops to Afghanistan to step up the fight against the resurgent Taliban.

The buildup of the 8,000 Marines and at least 4,000 Army troops will begin in the spring and last into the summer, and another 5,000 support personnel will follow, the Pentagon said. The additional forces will expand the US presence to more than 50,000 troops, with further waves of reinforcements expected later this year.

"The situation in Afghanistan and Pakistan demands urgent attention and swift action," Obama said in a statement. "The Taliban is resurgent in Afghanistan, and al-Qaeda supports the insurgency and threatens America from its safe haven along the Pakistani border."

The Obama administration is conducting a review of US strategy for the conflict in Afghanistan, where violence and instability have sharply worsened during the last two years. The top US commander in Afghanistan, General David McKiernan, has asked for an additional 30,000 troops.

Obama has vowed to wind down the US role in Iraq and shift more attention to Afghanistan, faulting predecessor George W Bush for invading the former and neglecting the latter.

"This increase is necessary to stabilize a deteriorating situation in Afghanistan, which has not received the strategic attention, direction and resources it urgently requires," Obama said.

There are about 34,000 US troops already in Afghanistan.

Obama said the latest orders to deploy will not interfere with the ongoing review. In an interview Tuesday with the Canadian Broadcasting Corporation prior to his visit to Ottawa on his first trip abroad, Obama said he will use all aspects of US power to prevail in Afghanistan.

"I am absolutely convinced that you cannot solve the problem of Afghanistan, the Taliban, the spread of extremism in that region, solely through military means," Obama said. "We're going to have to use diplomacy. We're going to have to use development."

Obama acknowledged that the conflict in Afghanistan "appears to be deteriorating at this point" but argued it is still "winnable."

He is scheduled to arrive Thursday in Ottawa for a short visit and meeting with Canadian Prime Minister Stephen Harper. Canada plans to pull all of its combat troops out of southern Afghanistan by 2011. The Obama administration has been hopeful that US allies would be willing to commit more troops.

Obama told CBC that he does not intend to arrive in Canada with specific requests.

"What I will be communicating is the approach that we intend to take," he said. "Obviously I'm going to be continuing to ask other countries to help think through how do we approach this very difficult problem. But I don't have a specific 'ask' in my pocket that I intend to bring out in our meetings." (dpa)