(Adds Syria fighting, Syrian gov't statement)
By Tuvan Gumrukcu and Lisa Barrington
ANKARA/BEIRUT, Oct 22 (Reuters) - Turkish-backed forces will press on to the Islamic State-held town of al-Bab in Syria, Turkish President Tayyip Erdogan said on Saturday, emphasising Ankara's drive to sweep militants and Syrian Kurdish fighters from territory near its border.
The Syrian military, however, said the presence of Turkish troops on Syrian soil was unacceptable and a "dangerous escalation and flagrant breach of Syria's sovereignty."
Backed by Turkish tanks, special forces and air strikes, a group of rebels fighting under the loose banner of the Free Syrian Army crossed into northern Syria in August and took the border town of Jarablus from Islamic State largely unopposed.
The rebels have since extended those gains and now control an area of roughly 1,270 square km (490 square miles) in northern Syria. While Turkey's initial focus was on driving Islamic State from Jarablus, much of its efforts have been spent on stopping the advance of U.S.-backed Syrian Kurdish fighters.
"They say, 'Don't go to al-Bab'. We are obliged to, we will go there," Erdogan said in a speech at the opening of an education centre in the northwest province of Bursa. "We have to prepare a region cleansed from terror."
Erdogan also said that Turkey would do what was necessary with its coalition partners in Syria's Raqqa, but would not work with the Syrian Kurdish fighters.
Differences over Syria have caused strains between NATO allies Turkey and the United States. Washington is backing the Syrian Kurdish YPG militia, seeing it as an effective partner in the fight against Islamic State. Turkey fears the militia's advance will embolden Kurdish militants at home.
The outlawed Kurdistan Workers Party (PKK) has carried out a three-decade insurgency that has killed more than 40,000 people, mostly Kurds, in Turkey's largely Kurdish southeast.
Both sides are supposed to be fighting Islamic State in Syria, but escalating clashes between them have highlighted the conflicting agendas of Ankara and Washington in the increasingly complex battlefield of northern Syria.
Since Wednesday, dozens of Turkish rockets and air strikes have pounded territory taken recently from Islamic State by Kurdish fighters allied to the U.S.-backed Syria Democratic Forces (SDF) militia, a monitor and militia spokesperson said.
Turkey's military on Saturday confirmed that it had hit 72 Islamic State and 50 Syrian Kurdish fighter targets in northern Syria by early Friday morning.
The British-based Syrian Observatory for Human Rights monitoring group said there was heavy fighting on Saturday on the frontline between Turkish-backed forces and Kurdish fighters allied to the U.S.-backed SDF militia west of Marea. Marea is a town in Turkey-backed rebel territory on the way to al-Bab.
The Observatory said around a dozen fighters on both sides have died in the past three days of escalating fighting.
If Turkey-backed rebels push further south through the current battleground with Kurdish fighters, they will come into contact with territory controlled by Syrian government and allied forces north of the city of Aleppo.
Statements from the Kurdish fighters on Saturday said an intense attack was being waged by Turkey-backed forces with tanks and heavy shelling. The Observatory and the Kurdish fighters said tanks had been seen crossing from Turkey from more than one border crossing.
The Syrian military said earlier this week it would bring down any Turkish war planes entering Syrian air space and reiterated its warning against Ankara on Saturday.
"The presence of Turkish military units inside the Syrian border is totally unacceptable in any form. We will deal with them as an occupying force and will confront them by all possible means," the Syrian Army General Command said. (Writing by David Dolan; Editing by Jeremy Gaunt and Helen Popper)