ISIS militants killed 10 Syrian troops and pro-government fighters in the former militant stronghold of Raqa province, a war monitor said Tuesday, displaying their ability to keep mounting deadly attacks.

Despite losing their last piece of territory in Syria in 2019, ISIS has maintained hideouts in the vast Syrian desert from which it has carried out ambushes and hit-and-run attacks.

“ISIS attacked positions and checkpoints belonging to the regime… setting fire to military vehicles and prefabricated houses,” the Syrian Observatory for Human Rights said.

Six soldiers were also wounded in the Monday evening attack, with some in critical condition, said the British-based monitor, which relies on a wide network of sources inside Syria.

Government troops control rural areas in the south and east of Raqa province, while Kurdish fighters control the rest.

The city of Raqa was the centre of the ISIS group’s brutal “caliphate” until Kurdish-led forces backed by the United States ousted them in 2017.

In March 2019, ISIS lost the last territory it held in Syria to a Kurdish-led counteroffensive backed by a US-led coalition, but militant remnants continue to carry out deadly attacks.

Targets have included civilians and Kurdish-led fighters as well as government troops and allied pro-Iranian militants.

Last week, the militants attacked a convoy of oil tankers guarded by the army in the Syrian desert, killing seven people including two civilians.

Last month, ISIS claimed responsibility for a rare bombing in Damascus that killed at least six people near the capital’s Sayyida Zeinab mausoleum.