An explosion shook the base of an al-Qaida-linked group in northern Syria on Tuesday, killing at least eight gunmen and wounding others, opposition activists said.

 

It wasn't immediately clear what caused the explosion at the base of Hayat Tahrir al-Sham in the northwestern province of Idlib, the last major rebel stronghold in the country, but some said it was a shell that exploded as fighters trained. HTS is the most powerful group in Syria's northwest.

 

The Britain-based Syrian Observatory for Human Rights said the explosion near the village of Ram Hamadan was apparently caused by a shell that exploded. The Observatory said eight fighters were killed and 10 were wounded.

 

It added that the explosion occurred as drones of the U.S.-led coalition were flying overhead.

 

Step news agency, an activist collective, said at least nine fighters were killed and others were wounded in the blast. Step said it could have been caused when a mortar shell exploded during training.

 

Hayat Tahrir al-Sham, Arabic for Levant Liberation Committee, has militarily crushed many of its rivals within the opposition, carried out a crackdown against the civilian population and set up its own so-called ``salvation government'' in 2017 to run day-to-day affairs in the region.

 

The group, which is led by Syrian citizen Abu Mohammed al-Golani, has been marking itself in recent years as a Syrian opposition group and distancing itself from al-Qaida.

 

Syria's 10-year conflict has left about half a million people dead and half the country's prewar population of 23 million displaced, more than 5 million of them as refugees outside the country.