The Cupertino company has been granted a new patent for "electronic devices with sidewall displays", filed in April of last year.

In May security forces sent in to clear the area found scores of children who had been forced into prostitution, and hundred of drug addicts.

Clashes between Turkey's security forces and the PKK resumed last year, ending a ceasefire.

Losing Sirte would be a major setback for the militants, already under pressure in Syria and Iraq.

The northern city of Aleppo, Syria's most populous before the war, is split into rebel- and government-held districts.