Busloads of Islamic State fighters stranded in the Syrian desert reached jihadist-held territory after the US-led coalition stopped surveillance of the convoy, a monitor said on Wednesday.

Coalition drones had been circling the stranded 11-vehicle convoy for days and periodically picking off IS fighters if they strayed too far from the vehicles.

But the convoy, with as many as 200 jihadists and 200 civilians on board, arrived in Deir Ezzor eastern Syria "after the coalition decision to stop their surveillance on the convoy", said the Syrian Observatory for Human Rights, a Britain-based monitor.

A source on the ground told AFP "the operation is done, Daesh (IS) convoy reached Deir Ezzor province".

The US-led coalition on Friday pulled aircraft from the skies above the convoy so regime and Russian forces could go past, officials said.

"To ensure safe deconfliction of efforts to defeat ISIS, coalition surveillance aircraft departed the adjacent airspace at the request of Russian officials during their assault on Deir Ezzor," the coalition said in a statement.

The vehicles left the Lebanon-Syria border region on August 28 under an evacuation deal negotiated between IS and the powerful Lebanese Shiite movement Hezbollah, which has intervened in the war in neighbouring Syria to prop up the Damascus government.

But the US-led coalition pounded the road to Deir Ezzor with air strikes to prevent the convoy reaching the IS-held town of Albukamal on the Iraqi border.

The United States has repeatedly stressed that it was not party to the Hezbollah deal and said the fate of those aboard the buses was not a coalition issue.