BEIRUT (Reuters) - The Syrian military on Sunday said one of its war planes had been downed in the eastern Syrian city of Deir al-Zor during an operation against Islamic state, where the militant group has been under intense air strikes in the past 24 hours.

The jet came down in the Jebel Tharda area which overlooks the government’s Deir al Zor military airport, the Syrian Observatory for Human Rights, which monitors the Syrian conflict now in its sixth year, said.

On Saturday U.S.-led coalition air strikes reportedly killed dozens of Syrian soldiers in Jebel Tharda, endangering a U.S.-Russian brokered ceasefire and prompting an emergency U.N. Security Council meeting as tensions between Moscow and Washington escalated.

A Syrian military statement said the plane had come down during an operation against Islamic State in Deir al-Zor and the pilot had died.

Islamic State-affiliated media said it had shot the jet down.

“A Syrian warplane belonging to the Syrian regime was brought down when targeted by fighters from the Islamic State in the city of Deir al-Zor,” Amaq said in an online statement.

The city’s military airport and some government-held districts have been entirely surrounded by Islamic State since last year, with the airport providing the only external access.

Intense air strikes over the past 24 hours have hit Islamic State controlled areas near Deir al Zor city, the Observatory and Syrian state media said.