Sunni rebels in Iraq say they have fully captured the country’s main oil refinery at Baiji, north of Baghdad.
The refinery had been under siege for 10 days with the militant offensive being repulsed several times.
US Secretary of State John Kerry is in Irbil, northern Iraq, for a second day of talks with the country’s leaders.
Insurgents, spearheaded by Islamists, have overrun a swathe of territory in the north and west including the second-biggest city, Mosul.
They are bearing down on a vital dam near Haditha and have captured all border crossings to Syria and Jordan.
The Baiji refinery, in Salahuddin province, supplies a third of Iraq’s refined fuel and the battle has already led to petrol rationing.
A rebel spokesman said the complex would now be handed over to local tribes to administer.
The spokesman said that the advance towards Baghdad would continue.
The US secretary of state vowed “intense and sustained support” for Iraq after meeting key politicians in the capital, Baghdad.
Mr Kerry said attacks by the Islamic State of Iraq and the Levant (Isis)were a threat to Iraq’s existence, and the next days and weeks would be critical.
Mr Kerry met Iraqi Prime Minister Nouri Maliki and also held talks with key Shia and Sunni figures.
Speaking at the US embassy, Mr Kerry said US support would “allow Iraqi security forces to confront [Isis] more effectively and in a way that respects Iraq’s sovereignty”.
“The support will be intense, sustained, and if Iraq’s leaders take the steps needed to bring the country together it will be effective,” he said.