CEYLANPINAR, Turkey >> Russia said today that its military units were patrolling territory in northern Syria between Syrian and Turkish forces after the U.S. withdrawal from the area, underscoring the sudden loss of U.S. influence in the area and illustrating how the power balance in the region has shifted rapidly in the past week.

The announcement that Russian forces were now patrolling an area where the United States had until Monday maintained two military bases appeared to signal that Moscow was moving to fill a security void left by the withdrawal of both the U.S. military and its partners in an international counterterrorism mission.

Videos circulating on social media appeared to show a Russian man filming himself walking around a recently evacuated U.S. military base in northern Syria.

The Russian Defense Ministry said in a statement that its military police, which had already established a presence in other parts of Syria, were patrolling “the northwestern borders of Manbij district along the line of contact of the Syrian Arab Republic military and the Turkish military.”

It added that its troops were coordinating “with the Turkish side” and that “the Syrian government army has taken full control of the city of Manbij and nearby populated areas.”

The developments today came as a spokesman for the U.S.-led coalition said on Twitter that its forces, which include French and British soldiers, had left the formerly Kurdish-held town of Manbij. “Coalition forces are executing a deliberate withdrawal from northeast Syria,” Col. Myles B. Caggins wrote. “We are out of Manbij.”

Russia and Turkey will shortly be the only international armies in the area.

Turkish and Syrian troops are racing to control large parts of northern Syria that were run by an autonomous Syrian Kurdish regional government until a Turkish-led invasion began Oct. 9, under the protection of U.S. troops stationed in the region.

Syrian government troops were deployed inside the northern city of Manbij, a Syrian state broadcaster said today, as Turkish-led forces advanced in the countryside outside the city.

Elsewhere in northern Syria today, Kurdish-led fighters attempted to retake the strategic border town of Ras al-Ayn from Turkish-led forces, as Kurdish and Syrian government troops sought to repel the Turkish incursion.

Heavy fire from machine guns could be heard to the south and southwest of Ras al-Ayn and from the Turkish border town of Ceylanpinar, which is less than a mile from the fighting. Turkish artillery pounded an eastern suburb of the Syrian settlement midmorning, raising clouds of smoke above low farmhouses and pistachio groves.

As of today, fighting in Ras al-Ayn and other areas in northern Syria has forced at least 160,000 people from their homes, according to United Nations estimates. Kurdish authorities put the figure at 270,000.

The battle highlighted the fluctuating nature of the Turkish incursion, which began after President Donald Trump ordered the evacuation of U.S. troops from the Turkish-Syrian border, opening the door for Turkish troops and their Syrian Arab proxies to enter Kurdish-held territory in northern Syria.

The White House decision drew global condemnation and left Kurdish fighters feeling betrayed, and the situation has quickly turned into a blood bath. Experts on the region warned that the withdrawal of U.S. troops would embolden Russia, Iran and the Islamic State group.

Abandoned by the Americans, and quickly losing land to the Turkish force, Kurdish authorities sought protection from the Syrian government and its largest backer, Russia.

Since Kurdish authorities asked the government of President Bashar Assad for assistance, thousands of Syrian Army troops have flooded into northern Syria for the first time since the government lost control of the region several years ago.

But Syrian government troops have stayed clear of the border region near Ras al-Ayn, where Kurdish troops fight on alone. Instead, government forces have deployed to other strategic positions, such as the western cities of Manbij, to help alleviate pressure on Kurdish fighters on the front line.

The last-minute alliance comes at great cost to Kurdish authorities, who are effectively giving up self-rule. Syrian Kurdish militias established a system of self-rule in northern Syria in 2012, when the chaos of the Syrian civil war gave them the chance to create a sliver of autonomous territory free of central government influence.

The fighters greatly expanded their territory after they partnered with an international military coalition, led by the United States, to push the Islamic State from the area.

After the Kurdish-led fighters captured Islamic State territory, they assumed responsibility for its governance, eventually controlling roughly a quarter of the Syrian landmass. They have also been guarding thousands of Islamic State fighters and their families, hundreds of whom fled a detention camp in Ras al-Ayn after Turkish-led forces bombed the surrounding area.The Kurds’ control of the land in Syria enraged Turkey, since the militia is an offshoot of a guerrilla group that has waged a decadeslong insurgency against the Turkish state. Turkey has long pressed the United States to abandon its alliance with Kurdish fighters so Turkish troops could enter Syria and force the Kurds from territory close to the border.

Washington rebuffed Turkey’s requests for several years, maintaining a de facto peacekeeping presence along the border near Ras al-Ayn, the town at the center of the fighting Friday. But that changed last week, when Trump made a sudden decision to withdraw troops — first from that particular area, and later from all of northern Syria.

In Britain, meanwhile, a day after foreign ministers from all 28 European Union member states agreed unanimously to stop selling arms to Turkey — the first time the bloc has reached such a decision about a NATO ally — Britain announced a pause in such ties with Turkey.

Dominic Raab, Britain’s foreign secretary, told the House of Commons on today that “no further export licenses to Turkey for items which might be used in military operations in Syria will be granted” until the government had conducted a review.

President Recep Tayyip Erdogan of Turkey has made clear he will not bow to pressure to halt the offensive.

“We will soon secure the region from Manbij to the border with Iraq,” he said today, during a visit to Azerbaijan, referring to the 230-mile expanse of territory.

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