ANKARA/ISTANBUL (Reuters) - Turkey-backed rebels may extend their zone of control in northern Syria by pushing south and are now targeting the Islamic State-held town of al-Bab, Turkish President Tayyip Erdogan said on Monday.

Free Syrian Army fighters launch a Grad rocket from Halfaya town in Hama province, towards forces loyal to Syria's President Bashar al-Assad stationed in Zein al-Abidin mountain, Syria September 4, 2016. REUTERS/Ammar Abdullah

Turkey’s “safety zone” in the region could eventually span an area of 5,000 square km (1,930 square miles), Erdogan told a news conference before departing for New York where he was due to address the United Nations’ General Assembly.

Ankara launched its operation in northern Syria known as “Euphrates Shield” last month, aiming to clear Islamic State from Turkey’s Syrian border area and to stop the advance of Syrian Kurdish fighters. So far, it has secured a thin wedge of land along its border.

“As part of the Euphrates Shield operation, an area of 900 square kilometers has been cleared of terror so far. This area is pushing south,” Erdogan said.

“We may extend this area to 5,000 square kilometers as part of a safe zone.”

Turkey has long argued for the need for a “safe zone” or a “no-fly” zone along its Syrian border, with the aim of clearing out Islamic State and Kurdish fighters and stemming a wave of migration that has fueled tensions in Europe.

But Western allies have so far balked at the idea, saying it would require a significant ground force and planes to patrol, marking a major commitment in such a crowded battlefield.

Erdogan said on Monday the Turkey-backed rebels - a group of Syrian Arabs and Turkmen fighting under the loose banner of the Free Syrian Army - were now focused on capturing the Islamic State-held town of al-Bab.

“Jarablus and al-Rai have been cleansed, now we are moving towards al-Bab... We will go there and stop (Islamic State) from being a threat to us,” he said.

CONTROL OF AL-BAB

Gaining control of al-Bab, which lies on the southern edge of what Ankara sees as its potential buffer zone, is crucial to Turkey’s plans to keep the Syrian Kurdish YPG fighters in check, analysts say.

Ankara’s challenge now is to turn the fractured Free Syrian Army into a coherent force as a counterweight to the YPG.

Turkey, a NATO member and part of the U.S.-led coalition against Islamic State in Syria, regards the Washington-backed YPG as a terrorist group and an extension of the outlawed Kurdistan Workers Party (PKK). Ankara worries that advances by the YPG will embolden insurgents in its largely Kurdish southeast.

Erdogan has frequently castigated the United States for its support of the YPG. On Monday he accused Washington of exacerbating tension in the region, referring to an incident last week when a small number of U.S. forces entered the town of al-Rai but were forced to withdraw after the Free Syrian Army rebels protested against their presence.

The U.S. special forces entered the town to coordinate air strikes against Islamic State.

“The Syrian army did not and does not want interference from U.S. special forces,” Erdogan said. “Unfortunately, the behavior of U.S. officials has pushed the FSA to this point,” he said, in what appeared to be a reference to Washington’s support of the YPG.

Separately, Turkey’s military said on Monday it hit Islamic State targets in northern Syria in air strikes a day earlier, targeting barracks and an ammunition store.

Erdogan said he plans to address the Syria crisis, the fight against terrorism and Turkey’s failed July 15 military coup when he addresses the U.N. General Assembly later this week.