Russian airstrikes have killed dozens of people in a Syrian coastal province, including a rebel commander who formerly served in President Bashar Assad's army, activists said.
The activists said the airstrikes, which began on Monday afternoon and lasted several hours, also wounded scores, making it one of the deadliest incidents since Russia began it aerial attacks nearly three weeks ago.
Since the airstrikes began, Syrian troops and their allies from Lebanon's Hezbollah militant group have launched ground offensives in northern, central and southern Syria as well as in the suburbs of the capital, Damascus, capturing areas formerly held by insurgents.
Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said at least 45 people were killed in the rebel-held Jabal al-Akrad region in Latakia province.
The Local Co-ordination Committees (LCC), another activist-run monitoring group, said 57 people were killed in the province on Monday, mostly by Russian airstrikes.
The Observatory and the LCC said the dead included army defector Basel Zimmo, who was the commander of the First Coastal Division, a rebel faction active in the area.
"The Russians are destroying all the fortifications before the attack on Jisr al-Shughour," Mr Abdurrahman said, referring to a strategic north-western town that insurgents captured earlier this year.
The Observatory, which relies on a network of activists inside Syria, said hundreds of Russian airstrikes over the past three weeks have killed 370 people, including 127 civilians. The group said the dead civilians included 36 children and 34 women.
The airstrikes also killed 243 fighters from different insurgent groups, including Islamic State (IS) and al Qaida's affiliate in Syria, the Nusra Front.
Russia has said its air campaign is aimed at helping the government defeat IS and other "terrorists" but many of the strikes have targeted Syrian rebels in areas where the extremist group is not present.
Jabal al-Akrad is close to the rebel-held north-western province of Idlib, which has been targeted by Russian warplanes since Moscow launched its air campaign late last month. Latakia province includes key strongholds of Assad and the Alawite religious minority to which he belongs.
Syria's conflict, which began in March 2011, has killed more than 250,000 people, wounded a million and displaced half the country's population.