President Recep Tayyip Erdogan on Sunday said Turkish troops and their Syrian rebel allies have entered the centre of the Islamic State-held bastion Al-Bab, saying its capture was just a "matter of time".

"Al Bab is now besieged from all fronts ... Our forces entered the centre" with Syrian rebels, Erdogan told journalists in Istanbul, adding it was "only a matter of time" before the allied forces took full control of the flashpoint town.