Fresh clashes are being reported between Sunni rebels and government forces around the city of Tikrit in Iraq.
Witnesses say there have been a wave of air strikes, including one which has reportedly hit the palace of former President Saddam Hussein.
The clashes come on the heels of the declaration of a caliphate, or Islamic state, by al-Qaeda offshoot, the Islamic State of Iraq and Syria.
Germany's foreign minister Frank-Walter Steinmeier is warning the declaration is a serious threat to the region.
"The advance of ISIS is a serious threat, of course, for the territorial integrity of Iraq, but in addition, also for the entire region. Everybody must be concerned that ISIS does not establish itself and that a hotbed of terror and violence does not develop in the declared so-called caliphate."
With brutal efficiency, the Sunni extremist group has carved out a large chunk of territory that has effectively erased the border between Iraq and Syria.
By declaring a caliphate, the group is now claiming leadership of the world's Muslims.
Iraqi analyst Ihsan al-Shamari suggests the declaration isn't likely to make much of a splash in the rest of the Muslim world.
"I think the declaration of the establishment of a new Islamic state won't have much resonance in reality, either in Iraq or abroad. The announcement called upon all Muslims to declare allegiance for Abu Bakr al-Baghdadi as a caliph for Muslims. The matter is linked to doctrines and ideologies. Anyhow, such an Islamic caliphate will never be supported worldwide."
Other observers are suggesting the declaration could trigger a wave of infighting among the Sunni militant factions that formed a loose alliance in the blitz across northern Iraq.
