BEIRUT — Five months of multi-sided clashes in Syria’s crowded northern battlefield have displaced some 66,000 people, a U.N. humanitarian agency said Sunday, a day after the U.S. bolstered Kurdish-led forces with a deployment of armored vehicles amid preparations for a push toward the Islamic State’s de facto capital.

Besides the autonomous Kurdish-led forces, Turkish, Syrian government and Syrian opposition fighters have all been jostling for territory formerly held by the Islamic State near the Turkish-Syrian frontier.

The U.S.-backed Syrian Democratic Forces, led by the Syrian Kurdish PKK party, are the current front-runners in the race to Raqqa, the Islamic State capital. They are now stationed five miles north of the Euphrates River city and supported by U.S.-led coalition airstrikes and a deployment of some 500 U.S. special forces operators. The Pentagon has said they are working in an advisory capacity.

But Turkey, a U.S. ally through NATO, says the PKK is an extension of the Kurdish insurgency inside its own borders and has classified the party as a terror organization. It has objected strongly over the SDF offensive and vowed to throw the Kurdish-led forces in Manbij – the SDF’s westernmost flank – back over the banks of the Euphrates. This would disrupt the Raqqa campaign.

There are Turkish forces stationed in al-Bab, 25 miles southwest of Manbij. The threats prompted the SDF to ask Russia and the Syrian army to establish a buffer between Manbij and al-Bab.

With uncertainty building, the U.S. deployed a number of armored vehicles to its allies in Manbij, the Syrian Kurdish Rudaw news agency reported Saturday.

Operation Inherent Resolve spokesman Col. John Dorrian confirmed the deployment on Twitter. He said it was meant to “deter aggression and keep focus on defeating ISIS,” another acronym for the Islamic State.

Dorrian said the deployment was there to guarantee that the Kurdish elements of the SDF have left Manbij.

The Syrian military, meanwhile, has driven east of Aleppo to draw a front with the Turkish-backed Syrian opposition forces south of al-Bab, blocking their route to Raqqa.