At least 25 civilians, including six children, were killed on Thursday in air bombardments in Syria's central Hama province, where rebels have advanced against regime forces in recent days, a monitoring group reported.
The Syrian Observatory for Human Rights added that unidentified warplanes had carried out more than 20 airstrikes on a road linking the village of Latamina in rural Hama and the southern countryside of Idlib in north-western Syria.
The intense bombing comes as rebels, including hardline Islamists, captured a string of regime-held villages and checkpoints in Hama countryside.
Syria's state news agency SANA said that airstrikes focused on "terrorist gatherings" in Hama's villages of Mork, Taybet al-Imam and Souran, leaving a "large number of terrorists" dead.
Brigadier Ali Kalouf, a senior army officer, was meanwhile killed in a fight against rebels in Mardes, north of Hama, the capital city of the province of the same name, the Observatory reported.
The rebels seized Mardes, nearby regime checkpoints and a missile battalion, according to the watchdog that relies on a network of activists inside Syria.
Russia, an ally of the Syrian government, planned to reinforce the facility and use it as a military base in the area, according to the Observatory.
The capture of Mardes has brought the rebels closer to Hama city.
The rebels are now around 10 kilometres from the Hama military airport, the Observatory said.
Activists in the area said rebels have seized several villages in the countryside of Hama from regime forces since August 29.
"The aim of the rebels' offensive is to control the countryside of Hama," Observatory head, Rami Abdel-Rahman, said.
He told dpa that regime jets and those of allied Russia were intensifying their raids in rebel-held areas in order to slow down rebels' advance.
Jund al-Aqsa, a hardline jihadist group of Syrian and foreign fighters, is the main force leading the attack on the rebel side in Hama. Moderate rebels are also taking part.
The rebel onslaught in Hama is named Marwan Hadid, after a Muslim Brotherhood-linked figure who died in a Syrian prison in the 1970s, highlighting the longstanding grievances of the Syrian opposition.
In 1982, Syria's then president Hafez al-Assad quelled a Muslim Brotherhood uprising in Hama city, killing thousands of people.
He is the father of incumbent President Bashar al-Assad who took power in Syria after Hafez's death in 2000.