WASHINGTON (Reuters) - The U.S. State Department has approved the sale of 5,000 Hellfire missiles to Iraq worth $800 million, the Pentagon said on Thursday.

Lawmakers have 30 days to block the sale, although such action is rare. The prime contractor on the deal would be Lockheed Martin Corp.

The Defense Security Cooperation Agency, which oversees foreign arms sales, told lawmakers the government of Iraq had asked to buy 5,000 of the air-to-ground missiles and 10 training missiles.

The missiles would contribute to the United States’ national security and “improve the Iraq Security Forces' capability to support ongoing combat operations,” the agency said in a notice to lawmakers posted on its website.

It said the deal would improve the Iraqi security forces' ability to fight Islamic State militants, who swept through a third of Iraq in 2014 to seize Mosul, the largest city in the north, and reach the vicinity of Baghdad.

A U.S.-led coalition spokesman recently said territory controlled by Islamic State militants had shrunk 40 percent from its maximum expansion in Iraq.

(Reporting by Idrees Ali; Editing by Bernadette Baum)