The insurgents, largely Sunni Muslims, said they were advancing into the ethnically diverse province of Diyala on Thursday - capturing the town of Dhuluiyah, just 90 kilometers (60 miles) from Baghdad.

A spokesman for the militants, who call themselves the Islamic State of Iraq and Syria (ISIS), Abu Mohammed al-Adnani vowed the group would press on to the capital.

Officials said three planeloads of Americans were evacuated from a major Iraqi air base in Sunni territory to the north of Baghdad. Among the first to be evacuated were military personnel who were stationed at the base training Iraqi forces to use fighter jets and surveillance drones. Hundreds of US contractors at the site were said to be still there.

The German Foreign Ministry said Germans should leave the governorates of Anbar, Ninevah and Salah al-Din - which have been either partially or completely overrun - because of the possibility of armed clashes there.

In a statement late on Thursday, it also urged citizens to leave Baghdad temporarily.

The ministry went on to describe the situation in the provinces of Diyala and Kirkuk as "extremely alarming."

Meanwhile, the Turkish prime minister's office said on Thursday that an intensive diplomatic effort was underway to free 80 Turkish citizens held by militants in Mosul.

Iraqi Prime Minister Nuri al-Maliki's request for a state of emergency failed, as proceedings were adjourned due to a lack of a quorum in parliament.

500,000 people forced to flee

The Shiite-led government in Baghdad has been completely outflanked by the jihadist onslaught, which has declared Shariah law in swathes of the north, including Iraq's second largest city, Mosul. Some 500,000 people were reported to have fled amid fighting in and around the city, which was taken on Tuesday.

Iraqi forces were reported to have launched air strikes on jihadist positions in and around the cities of Mosul and Tikrit.

Senior intelligence sources told the AP news agency that members of late Iraqi leader Saddam Hussein's regime - including a force led by Hussein's former deputy Izzat Ibrahim al-Douri - were fighting alongside ISIS.

Government troops are also reported to have melted away in the face of an attack by autonomous Kurdistan's peshmerga fighters, who seized the disputed oil city of Kirkuk.

rc/pfd (AFP, AP, dpa, Reuters)