Members of the Islamic State and their families are seen in a bus in Qara area in Syria's Qalamoun region on Aug. 28. (Louai Beshara/AFP/Getty Images)

At Russia's request, the U.S. military on Friday called off its surveillance of a convoy of Islamic State fighters that has been stuck in the Syrian desert for the past 10 days, saying it is now up to the Syrian government to resolve its fate.

The decision to withdraw the warplanes that have been circling over the convoy came after Syrian troops advancing through the province of Deir al-Zour passed the point where the convoy is located, leaving it behind Syrian army lines, according to a military statement.

The convoy became stuck in the no man's land between the front lines of the Syrian army and the Islamic State after the U.S. military bombed the road ahead to prevent it from reaching Islamic State territory in eastern Syria. It had been traveling there from western Syria under the terms of a deal struck between the Islamic State and the Lebanese Hezbollah movement to end fighting along the Lebanese border.

Because Syrian troops are now in control of the area, the U.S.-led coalition against the Islamic State agreed to a Russian request to halt the surveillance, in the interests of deconflicting the rival Russian- and U.S.-backed efforts to defeat the militants, the statement said.

The military added that it would continue to try to prevent the militants aboard the buses from reaching Iraq.

"The regime's advance past the convoy underlines continued Syrian responsibility for the buses and terrorists," said Brig. Gen. Jon Braga, director of operations for the U.S.-led coalition. "As always, we will do our utmost to ensure that the ISIS terrorists do not move toward the border of our Iraqi partners."

U.S. military officials had previously said that they would not allow the buses to reach any Islamic State-controlled area, in Syria or Iraq. It is unclear whether the Syrian advance into the area means the terms of the Hezbollah-brokered deal will now be fulfilled and the buses will be allowed to proceed to their original destination, the Syrian border town of Bukamal.

The original convoy of 17 buses loaded with Islamic State fighters and their families had already broken up, with six managing to head back into Syrian government territory and 11 getting stuck after the bombing of the road. The U.S. military did not bomb the convoy itself, because of the presence of women and children.

There were several reports that some individual fighters managed to escape across the border into Iraq, and Hezbollah said in a statement Saturday that some buses had made it into to Islamic State territory, without giving details. An official linked to Hezbollah said the number was four.

But the U.S. military said it was sure no buses made it into militant-controlled areas. The military also said it killed 85 fighters in the vicinity of the buses who were attempting to escape.

Suzan Haidamous in Washington contributed to this report.

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