A suicide bomber set off his explosives late on Thursday in northwestern Syria, killing the co-founder of the country’s main al-Qaida-linked group that controls much of the northwest, a war monitor said. Some activists disputed the source of the explosion, saying instead that a remotely detonated bomb killed Abu Maria al-Qahtani, whose real name was Maysara al-Jubouri. Al-Qahtani co-founded the Nusra Front in Syria, a militant group that later renamed itself Hayat Tahrir al-Sham and claimed it had severed ties with al-Qaida.

The conflicting accounts could not immediately be reconciled.

According to the Britain-based Observatory for Human Rights, a war monitor with a network of activists on the ground, the bomber entered al-Qahtani’s guesthouse in the town of Sarmada in Idlib province late in the evening and detonated his explosives.

The small enclave of northwestern Syria is the country’s last rebel-held territory. Hayat Tahrir al-Sham controls the northwestern Idlib province while Turkey-backed opposition groups control northern Aleppo province. Most of the 4.5 million people living in Idlib and Aleppo provinces rely on humanitarian aid to survive, and almost half live in displacement camps

The killing of al-Qahtani came against the backdrop of protests against his group and its leader, Abu Mohammed al-Golani, over the militants’ harsh reign over the region and deteriorating economic conditions.

He was released from jail in March after being detained by his own men in August over misuse of social media. According to the Observatory, he was accused of communicating with hostile groups. He had since been dismissed from his duties as a senior official for the group. The Observatory said that shortly after the explosion, al-Qahtani was rushed to Bab al-Hawa Hospital in Idlib but died of his wounds. According to the war monitor, two of guests at al-Qahtani’s house were also wounded. However, a medical official told The Associated Press that al-Qahtani’s escort and eight other guests were wounded, nine in all. The official spoke on condition of anonymity because he was no authorities to talk to the media.

Public sentiment against al-Golani and Hayat Tahrir al-Sham has been rising since the militant group cracked down on senior members and suppressed street protests.

Al-Qahtani, an Iraqi citizen, had been a longtime al-Qaida member who fought against US forces in Iraq following the 2003 US-led invasion that toppled dictator Saddam Hussein. In 2011, he was one of several al-Qaida figures who moved to Syria, months after the country’s ongoing deadly conflict began.