Turkish soldiers approach people demonstrating in support of Syrian Kurds as fighting intensified between Syrian Kurds and the militants of Islamic State, in Kobani, Syria, in Mursitpinar near Suruc, Turkey, October 4, 2014. (AP)

Washington, Reuters—The United States and Turkey are closing in on a deal that will allow the US military and allied forces to use Turkish air bases in their campaign against Islamic State of Iraq and Syria (ISIS) militants in Syria, the Wall Street Journal reported on Monday.

The newspaper, citing US and Turkish officials, said the agreement could include a safe zone along a portion of the Syrian border to protect refugees and certain opposition forces that would also “be off-limits” to aircraft from Syrian President Bashar Al-Assad’s government.

Allowing the United States and its allies to use Turkey’s bases would allow the coalition forces another foothold from which to launch continued strikes against the militants.

Turkey has agreed to allow 2,000 opposition fighters to be trained within its borders and has sent Turkish special forces to Iraq to train Kurdish peshmerga fighters, the report said.

The potential deal represents a narrowing of differences between the two sides as the United States and its coalition of allies continue to launch air strikes against ISIS militants in Syria and Iraq.

According to the Wall Street Journal, the agreement moves away from a larger formal “no fly” zone sought by Turkish officials covering a wider swath of northern Syria.

A protected zone along the Turkish-Syrian border would help safeguard opposition fighters being trained in Syria and shield opposition supply lines, the report said.

Under the deal, the US-led coalition “could send a quiet warning to the Assad regime to stay away from the zone or risk retaliation,” the Wall Street Journal said.

The report follows US Vice President Joe Biden’s visit to Turkey last week that aimed to smooth differences in the fight against ISIS militants, who have declared an Islamic “caliphate” in the parts of Iraq and Syria where they have seized control.

Biden had concluded two-days of meetings, including one with Turkish President Tayyip Erdogan, with no guarantee of Turkey’s military cooperation.

The paper said Turkish officials are considering invoking Ankara’s right to self defense under the United Nations charter by writing to the UN in order to justify the use of its bases. That could allow other North Atlantic Treaty Organization allies to join the fight against ISIS militants, it said.