"I will seek authorisation for the use of force from the American people's representatives in Congress," President Obama said.
He said Congressional leaders agreed to "schedule a debate and then a vote as soon as Congress comes back in session."
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Tony Davies was the first civilian to reach Pc Palmer after he was stabbed during the Westminster attack.
Defiant Londoners put on a show of solidarity for the victims of the Westminster terror attack at a vigil in their honour.
Weather set to improve with plenty of sunshine by Saturday