An Al Qaeda offshoot led an offensive on Monday against regime forces in north-west Syria, sparking clashes that killed 19 pro-government fighters and 22 extremists, a war monitor said.
"Extremist factions led by Hurras Al Deen launched an assault on two villages in Sahl Al Ghab," a region of the central province of Hama, the Syrian Observatory for Human Rights said.
They briefly seized the villages of Al Fatatra and Al Manara, Observatory chief Rami Abdulrahman said from Britain.
But regime forces took them back just hours later amid Russian air strikes and intense shelling, the monitor said.
The country's official Sana news agency also reported the attack on "two Syrian army positions," saying it involved "explosive-rigged vehicles and suicide bombers".
It quoted a military source as saying the situation was now under control after the extremists were forced to pull out under regime fire.
The offensive was launched from within the Idlib region, which is controlled by militants and rebels, and is the last bastion of resistance to Damascus after nine years of devastating civil war.
A truce reached on March 6 has largely stemmed fighting in the region, which President Bashar Al Assad has vowed to fully retake.
Hurras Al Deen is a relatively small but powerful armed group led by Al Qaeda loyalists.
It is a rival of Hayat Tahrir Al Sham, an alliance of militant factions dominated by former members of Al Qaeda's ex-Syria affiliate Jabhat Al Nusra, although the groups co-operate at times.
The Idlib truce brokered by regime ally Russia and rebel backer Turkey has largely kept Syrian and Russian warplanes out of the region's skies.
The calm came as the novel coronavirus pandemic spread across the Middle East.
Aid groups had warned that an outbreak of the Covid-19 illness in the Idlib region could cause a humanitarian disaster of previously unseen proportions.
