President Barack Obama will send an extra 4,000 US troops to Afghanistan to help train the country's forces.
Mr Obama is unveiling a new US strategy for the war designed to turn the tide against a growing insurgency, the White House said.
The move to deploy an extra brigade follows President Obama's decision last month to send in 17,000 reinforcements to take on insurgents challenging the Kabul government.
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The new troops will be deployed "later this year" to train local police and security forces, a defence official said.
There will be 61,000-65,000 troops in the country by mid-September with the arrival of various support units.
It doubles America's military presence in Afghanistan from December.
