(Adds White House, Canadian comment)
WASHINGTON, Jan 15 (Reuters) - The United States will send an additional force of about 3,200 Marines to Afghanistan this spring to help NATO troops and Afghan security forces confront rising Taliban violence, the Pentagon said on Tuesday.
The U.S. troop expansion, which increases the number of U.S. forces deployed to Afghanistan by more than 10 percent, follows months of unsuccessful U.S. efforts to persuade NATO allies to provide extra combat forces.
A Pentagon spokesman insisted that the deployment did not eliminate the need for more NATO troops and the effort to persuade allies to send more forces would go on.
Violence has surged in Afghanistan over the past two years, with the hard-line Islamist Taliban fighting a guerrilla war in the south and east and carrying out high-profile suicide and car bombings across the country.
Extra U.S. combat forces are needed to help thwart an expected offensive by Taliban militants as snows melt in the coming months, U.S. defense officials say.
President George W. Bush approved the Marine deployment on the recommendation of Defense Secretary Robert Gates.
The Pentagon said 2,200 troops from the 24th Marine Expeditionary Unit would be sent in March to serve under the NATO-led International Security Assistance Force (ISAF) in southern Afghanistan, where the Taliban resistance is strongest.
About 1,000 Marines from another battalion will deploy in April to expand training for Afghan national security forces.
TALIBAN, AL QAEDA THREAT
"President Bush is committed to seeing an Afghanistan that is free of the Taliban and al Qaeda and has an army and security force that can defend the country. These additional Marines will help defeat extremists that threaten all of us," White House spokesman Gordon Johndroe said.
Analysts said the Bush administration had found it could not get NATO allies to provide a large share of extra combat forces needed in southern Afghanistan to help clear and retain territory taken from militants.
"NATO's need is in the south at the moment. But what the U.S. has found is that most NATO countries are not willing to deploy forces to conduct combat operations where they're needed most," said Seth Jones, an Afghanistan expert at RAND Corp.
Pentagon spokesman Geoff Morrell said the deployment would not eliminate the need for troops from NATO allies. "We've made it clear that this is seven months. This is a one-time deal, that's it," he told reporters.
"Beyond that we are going to need our allies' help to either back-fill this deployment or perhaps match us in the numbers we're putting forth now," Morrell added.
Canada, which has about 2,500 combat troops in Afghanistan's southern Kandahar province, welcomed the Marine deployment. "This would allow us to have the assets available to be able to expand into some of the key areas," a Canadian official told reporters.
The prospect of sending forces into combat is too politically sensitive for some NATO countries, while others believe the battle against the Taliban can best be waged through development rather than military force, analysts said.
The United States has about 27,000 troops in Afghanistan -- the most since leading the 2001 invasion. About half serve in a 40,000-strong NATO-led force, while the rest conduct missions ranging from counterterrorism to training Afghan troops. (Additional reporting by Paul Eckert in Washington, Tabassum Zakaria in Riyadh and David Ljunggren in Ottawa) (Editing by Patricia Wilson and David Storey)
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