Reports say fighting between security forces and Sunni militants was continuing on June 20 at Iraq's largest oil refinery at Baiji, north of Baghdad.
The militants -- led by the Islamic State of Iraq and the Levant (ISIL) -- besieged the refinery earlier this week as they pushed toward the capital after capturing swaths of territory in the north.
President Barack Obama said on June 19 the United States would send up to 300 military advisers to help the fight against the militants.
He said U.S. combat troops will not be returning to fight in Iraq.
Iraq's Shi'ite-led government has asked Washington for air strikes against the Sunni militants.
Obama said he is prepared to take "targeted" military action "when and if" necessary.
But he insisted there was no military solution and called on the government to be "inclusive."
Based on reporting by Reuters and AP