At least 1,600 people were killed in Syria last week, making it the deadliest week yet in the civil war, a UNICEF spokesman said Sunday.
Patrick McCormick of the U.N. children's fund said the toll included children, as the government of Bashar al-Assad fights to suppress an 18-month uprising against its rule.
Nearly 5,000 people died in August, according to the Center of Documentation of Violation in Syria, which put the toll for the month at 4,937.
And there appeared to be no letup in the violence on Sunday, with opposition sources saying at least 144 people were killed across the country.
The Local Coordination Committees of Syria, an opposition group, said the toll includes a "massacre" of 35 people in the village of Al Fan in Hama province.
The state news agency SANA said there had been a clash between government forces and an "armed terrorist group" in the area.
Separately, a bombing near a government security building in the capital Damascus left at least four people wounded, state television said, calling the incident "terrorism."
The opposition Free Syrian Army's Grandsons of the Prophet Brigade said it carried out the attack.
CNN cannot independently verify reports of violence, because the Syrian government limits access by international journalists.
Opposition fighters claimed Saturday to be making advances, saying they captured a military air force base after an 11-day siege.
They seized the base to prevent airstrikes and shelling of civilians, Ridha Al-Alwani said via Skype from the border city of Albu Kamal in Deir Ezzour province.
A Free Syrian Army spokesman said the installation was the Air Defense battalion headquarters in Albu Kamal.
The military, however, still controls two other bases that it used to launch airstrikes following the rebel attack, Al-Alwani said.
At least 162 people died across Syria on Saturday, including 55 in and around Damascus, opposition activists said.
Several political activists reported that regime forces raided a hospital in the Damascus suburb of Kafar Batna, killed medical staff, and wounded patients. They said regime forces later burned the hospital.
The Local Coordination Committees of Syria said the regime forces had targeted the hospital in the past because it treated protesters.