Coalition forces in Syria are reinforcing their garrison near al-Tanf border crossing amid a buildup of pro-regime troops nearby, AFP reported Thursday (June 1st).

"We have increased our presence and our footprint and prepared for any threat that is presented by the pro-regime forces," said coalition spokesman US Col. Ryan Dillon.

Al-Tanf, on the key highway connecting Damascus with Baghdad, has been menaced by a surge of Iran-backed troops loyal to the Syrian regime. The area, just north-east of the Jordanian border, is used by coalition forces as a training and staging area for attacks against the "Islamic State of Iraq and Syria" (ISIS).

Coalition planes on May 18th pounded the front of a regime convoy that had apparently been headed toward the al-Tanf garrison.

That strike occurred inside an established "deconfliction zone" covering a 55-kilometre radius around the base. The Pentagon said it appeared that the regime troops were trying to build a "fire base" for artillery units inside the zone.

Last weekend coalition planes dropped leaflets warning the pro-regime troops to stay away.

Dillon said there are about 200 coalition and partner forces in the area and that support for them has been beefed up.

"We have constant coverage over our forces there in al-Tanf," he said.