Fresh clashes have been reported between jihadist-led Sunni rebels and government forces around the Iraqi city of Tikrit.
Witnesses said there had been a wave of air strikes and that former President Saddam Hussein’s palace had been hit.
A local source told the BBC the rebels had meanwhile seized parts of a nearby military base in a counter-attack.
It comes a day after the Islamic State in Iraq and the Levant (Isis) announced the creation of a “caliphate”.
The rebels reportedly seized control of parts of the Speicher army base to the north of the city, despite coming under attack from government helicopters.
The Iraqi army denied reports that the rebels had driven back a convoy coming to the aid of the base.
Tikrit was seized by Isis-led militants on 11 June as they swept across large parts of northern and western Iraq, and has been the scene of fierce clashes between the two sides in recent days.
On Friday, soldiers recaptured part of the campus of Tikrit University. An offensive over the weekend met stiff resistance and soldiers were said to have had to pull back to the town of Dijla.
On Sunday, Isis said it was establishing a caliphate, or Islamic state, on the territories it controls in Iraq and Syria.
It also proclaimed the group’s leader, Abu Bakr al-Baghdadi, as caliph and “leader for Muslims everywhere”.
Setting up a state governed under strict Islamic law has long been a goal of many jihadists.
Isis also said that from now on it would be known simply as “the Islamic State”. Abu Bakr al-Baghdadi, the group said, would be referred to as “Caliph Ibrahim”.
iv on Sunday, he said the Kurds were “a nation of fighters and have proved political commitment and are worthy of independence”.
The Kurds have long striven for an independent state but they remain divided between Syria and Turkey, Iran and Iraq.
The international community, including neighbouring Turkey and the US, remains opposed to the break-up of Iraq.