NATO Secretary-General Anders Fogh Rasmussen called on Monday, June 16, for the immediate release of Turkish diplomatic and security staff held by insurgents in the northern Iraqi city of Mosul.

"We want to see all of the Turkish hostages released and we want to see them safe," Rasmussen said in a statement during a visit to Ankara after a meeting with Turkish Foreign Minister Ahmet Davutoglu, according to Reuters.

Sunni insurgents seized a mainly ethnic Turkmen city in northwestern Iraq on Sunday after heavy fighting, solidifying their grip on the north after a lightning offensive that threatens to dismember the country.

Residents reached by telephone in the city of Tal Afar said it had fallen to the rebels from the Islamic State of Iraq and the Levant after a battle that saw heavy casualties on both sides.

"The city was overrun by militants. Severe fighting took place, and many people were killed. Shi'ite families have fled to the west and Sunni families have fled to the east," said a city official who asked not to be identified.