BEIRUT (AP) — Gunmen ambushed a bus carrying Syrian soldiers early Friday in the country’s east, killing at least 20 and wounding others, opposition activists said.

The attack was believed to be carried out by members of the Islamic State group whose sleeper cells in parts of Syria still carry deadly attacks despite their defeat in 2019.

The Britain-based Syrian Observatory for Human Rights said 23 Syrian soldiers were killed and 10 were wounded in the attack on a desert road near the eastern town of Mayadeen in Deir el-Zour province that borders Iraq.

Another activist collective that covers news in eastern Syria said 20 soldiers were killed and others were wounded.

There was no immediate comment from the Syrian army or government on the attack.

IS controlled large parts of Syria and Iraq where they declared a caliphate in June 2014. Over the years they lost of the land and were defeated in Iraq in 2017 and two years later in Syria.