Erdogan says Turkish troops inside Syria's al-Bab

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 before leaving for a tour of Bahrain, Saudi Arabia and Qatar. 

Erdogan said it was "only a matter of time" before the allied forces took full control of the flashpoint town.

"Daesh forces have begun leaving al-Bab completely," he said, using an Arabic acronym for the Islamic State (IS) group.

Erdogan also said that the final goal of the Turkish military incursion into Syria was not just to retake the city of al-Bab from IS, but to cleanse a border region - including the IS de facto capital, Raqqa - of the militants.

"The ultimate goal is to cleanse a 5,000 sq km area," Erdogan told the news conference.

"Daesh's main centre is not al-Bab but Raqqa," he said. "Once Raqqa is cleared, this region will be a terror-free area."

Civilian death toll rising

Six civilians were killed in Turkish shelling of al-Bab on Sunday, bringing the total number of civilian deaths since the assault on the city began to 370, according to the Syrian Observatory for Human Rights.

Turkey has long advocated a "safe zone" for civilians in northern Syria cleared of IS militants and the Kurdish YPG militia, but has said such an area would need to be policed by a no-fly zone.

Erdogan said he had discussed this again with the United States and Russia, and that Turkey was prepared to do the infrastructure work in the zone, to help prevent migration from Syria and allow those who had fled to Turkey to go home.

Turkish forces and allied rebels on Saturday entered al-Bab to drive IS militants from the flashpoint northern town, the Observatory said. 

The Turkish army launched an ambitious campaign inside Syria on 24 August, codenamed Euphrates Shield, to rid its border from IS militants and stop the advance of Kurdish militia. 

But the clashes in al-Bab have proved the toughest in the campaign, with Turkish military fatalities surging.

One Turkish soldier was killed and three others wounded in clashes with militants on Sunday, the private Dogan news agency reported, citing military sources.

The latest casualty raised the number of Turkish troops killed in the Syria offensive to 67.

The three injured troops were evacuated from al-Bab and taken to hospitals in Turkey's Kilis and Gaziantep provinces near the Syrian border, Dogan reported. 

Al-Bab is the militant group's last stronghold in the northern province of Aleppo and is also being targeted by Syrian government forces.