Turkey has warned it will retaliate if any of its 80 nationals kidnapped by insurgents in northern Iraq are harmed.

The group of people seized by the Islamic State of Iraq and the Levant (ISIL), an al-Qaeda offshoot group, includes special forces soldiers, diplomats and family members.

NATO has held an emergency meeting in Brussels at Turkey’s request. Prime Minister Recep Tayyip Erdogan and President Abdullah Gul held crisis talks with military and intelligence chiefs.

Turkish Foreign Minister Ahmet Davutoglu cancelled meetings at the UN to return to Turkey.

“The most important thing is the safe and secure return of our personnel and their families to Turkey. In Syria or Iraq or anywhere in the world, those who jeopardise the lives of our people will receive the harshest retaliation. Nobody should test the determination and capability of Turkey,” said Davutoglu.

The United States has pledged any “appropriate assistance” to help the Iraqi government fend off a rapid military advance by Sunni militants.