At least 25 people have been killed and 25 more injured, some critically, after a suicide bomber detonated his explosive vest on a bus in Syria's Idlib province, adjoining Turkey, according to a monitoring network.
The Syrian Observatory for Human Rights said the bus was carrying opposition fighters when the blast happened near the Atmeh border crossing.
Turkey's CNN Turk television citing local sources reported that the explosion occurred at the entrance of Atmeh refugee camp in Idlib late on Sunday.
Turkey sent several ambulances to the scene of the attack; eight injured rebels who were in critical condition were taken to hospitals in Turkey's Hatay province.
The rest are being treated in Syrian hospitals, Turkish media reported.
Authorities in Hatay said in an official statement on Monday that four of the injured fighters later died in Turkish hospitals.
Idlib is a major bastion of the Turkey-backed opposition to President Bashar al-Assad's rule.
The Syrian observatory had earlier reported 26 air strikes on Sunday across the province.
Rami Abdurrahman, the observatory head, said Russian and government air strikes have intensified since rebels launched a campaign on July 31 from Idlib to break a government siege of Aleppo's opposition districts.
The raids have killed scores of civilians, he said.
'Staggering death tolls'
More than 180 civilians have been killed across Syria since Friday, including 22 children and 23 women, the Local Coordination Committees, a grassroots network of activists, said on Sunday.
At least 90 people were killed on Friday, while a further 83 civilian deaths were recorded by Saturday night, with most of them occurring in Aleppo province.
"Even with the deadly standards of this war, these death tolls are staggering," Al Jazeera's Reza Sayah, reporting from Gaziantep on the Turkish side of the Syria-Turkey border, said.
The Syrian observatory also released figures on Sunday detailing the killing of at least 327 civilians, including 76 children and 41 women, in Aleppo over the last 15 days.
More than 100 of the 327 were reportedly killed in bombing by government warplanes, while 126 were killed in attacks by opposition fighters on government-held areas in Aleppo.
In the suburbs of the city, another 94 were killed by Syrian regime bombardments, according to the observatory.
Source: Al Jazeera And Agencies