WASHINGTON (Reuters) - The Republican chairman of the House of Representatives Armed Services Committee said on Monday that President Barack Obama must ask Congress for additional funds to pay the deployment of more troops to Iraq, as Congress and the White House debate defense spending amid mandatory budget cuts.


"Added to the President's Afghanistan announcement last week, the United States will now be deploying thousands more troops than we have budgeted for in the President's budget request," Representative Mac Thornberry said in a statement.


"Those deployments can only be fully supported through a supplemental budget request," Thornberry said.


U.S. Defense Secretary Ash Carter announced on Monday that Washington would send 560 additional troops to assist Iraqi forces in an expected push on the Islamic State stronghold of Mosul. Obama said on July 6 he would keeping 8,400 troops in Afghanistan through the end of his presidency in January.


As the Republican-led Congress and the Democratic administration grapple over spending, Obama has threatened to veto a $602 billion defense policy bill because of its use of special funds for the wars in Afghanistan and Iraq to avoid mandatory spending limits.


Democrats say the Department of Defense should be subject to the same spending restrictions as non-military programs, but Republicans accuse Democrats of stinting on national security in order to fund pet projects.

(Reporting by Patricia Zengerle; Editing by Jonathan Oatis)