Syrian troops have entered a town that was taken from Islamic State by Kurdish forces, in an apparent alliance to fend off Turkey-backed rebels.Turkey-backed fighters said their forces were ready to fight for Manbij, a target they have been seeking to acquire for some months.US-backed Syrian Defence Forces, many under the banner of Kurdish People's Protection Units, took Manbij from IS after bitter fighting in 2016.Image:Syria Democratic Forces (SDF) fighters walk through Manbij after defeating IS in 2016An offensive against Manbij by Turkey-backed Syrian rebels would comes days after Donald Trump said US troops were pulling out of Syria.The US is yet to start removing its forces but it is understood rival groups in the area are readying themselves to grab territory American forces vacate.Turkey-backed rebel spokesman Youssef Hammoud said: "We are in forward positions all along the front line with Manbij and rural areas.Image:Turkish soldiers in the countryside around Manbij"We have reinforced our positions and are on alert, awaiting the signal for the start of the battle."Syria's military said it had entered Manbij in an apparent deal with the Kurds but American troops patrolling the town denied there was any change of forces in the contested area.There were conflicting reports on the exact location of the Syrian troops, who said they had moved into Manbij and raised the Syrian flag in the town.Image:Turkish-backed Syrian fighters warm up around a fire at a position near ManbijThe Kurdish militia said it had invited the Syrian government to take control of Manbij to protect it against "a Turkish invasion".A Kurdish official said a deployment by forces loyal to Syrian President Bashar al Assad has so far been limited to the front line with Turkey-backed fighters, based north and west Manbij.Officials in Washington, meanwhile, said Syrian regime forces and some Russian forces had moved a bit closer to the city but were largely south or southwest of the city.Image:US forces' vehicles and structures on the outskirts of ManbijAnalysts said the Kurds' invitation to Syrian troops shows they'd rather let the Syrian government fill the void left by the Americans, than face being overwhelmed by those backed by Turkey.Turkey considers the Kurdish People's Protection Units, which now control nearly 30% of Syria, a terrorist group linked to the PKK, which has been responsible for various acts of violence on Turkish soil.Turkey's President Recep Tayyip Erdogan called the move by Syrian forces "a psychological act".Image:A Syrian man walks in a bazaar in the northern Syrian town of ManbijKremlin spokesman Dmitry Peskov called it a "positive step" that could help stabilise the areaRepublican Senator Lindsey Graham tweeted that the reports about Kurds aligning with Mr Assad were a "major disaster in the making".Ilham Ahmed, a senior Kurdish official, said work was under way to come to an arrangement with the Russians and the Syrian government.