President Barack Obama, in his first major military decision as commander-in-chief, has ordered 17,000 more troops to Afghanistan to tackle an intensifying insurgency, the White House said on Tuesday.
But in an interview with Canadian Broadcasting Corporation (CBC), Obama also said military means alone would not solve the problem.
U.S. officials have said Washington and its allies are not winning in Afghanistan, more than seven years after toppling the Taliban for giving sanctuary to al Qaeda leaders responsible for the September 11 attacks on the United States in 2001.
The extra 17,000 troops will increase the U.S. military presence in Afghanistan by more than 40 percent.
"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 in a statement.
But in an interview with CBC Television ahead of a visit to Canada, Obama said: "I’m absolutely convinced that you cannot solve the problem of Afghanistan, the Taliban, the spread of extremism in that region, solely through military means.
"We’re going to have use diplomacy, we’re going to have to use development, and my hope is that in conversations that I have with (Canadian) Prime Minister (Stephen) Harper that he and I end up seeing the importance of a comprehensive strategy."
The new forces will include a Marine expeditionary brigade of some 8,000 troops and an Army brigade of 4,000 soldiers equipped with Stryker armored vehicles, the Pentagon said.
"The decision was communicated to the Pentagon yesterday. The orders were signed today," White House spokesman Robert Gibbs told reporters traveling with Obama in Denver.
The extra forces will go to southern Afghanistan, where U.S. and NATO troops have struggled to hold territory against an increasingly bold Taliban insurgency.
The forces are part of an anticipated build-up that could expand the U.S. military presence in Afghanistan to 60,000 troops, from a current 38,000.
As well as American forces, there are also some 30,000 troops from NATO nations attempting to stabilize Afghanistan.
"There is no more solemn duty as president than the decision to deploy our armed forces into harm’s way," Obama said. "I do it today mindful that the situation in Afghanistan and Pakistan demands urgent attention and swift action."
U.S. officials say Taliban safe havens over the border in Pakistan are a major asset for insurgents.
The announcement comes while the White House is still conducting a broad review of U.S. policy on Afghanistan.
The deployment provides two of three extra combat brigades requested by the top U.S. and NATO commander in Afghanistan, Army General David McKiernan.
The units had originally been scheduled to go to Iraq.
Obama has pledged to pull out all U.S. combat troops from Iraq within 16 months, but commanders are pushing for a slower withdrawal, warning that security gains are fragile.
Both Democrats and Republicans welcomed Obama’s decision to send more troops to Afghanistan.
Senator John McCain, the Arizona Republican defeated by Obama in last November’s presidential election, described the situation in Afghanistan as "dire." But he also called on Obama to spell out a clear strategy.
"There still exists no integrated civil-military plan for this war — more than seven years after we began military operations," McCain said. "A major change in course is long overdue."
(Additional reporting by David Morgan in Washington, Caren Bohan in Denver and Randall Palmer in Ottawa)