BEIRUT — Activist groups said Sunday that about 5,000 people were killed in Syria's civil war in August, the highest figure reported in more than 17 months of fighting, as President Bashar Assad's regime unleashed crushing air power against the revolt.
The U.N. children's fund UNICEF put the death toll for last week alone at 1,600, the largest weekly figure for the entire uprising.
"The past month witnessed large massacres, and the regime was conducting wide operations to try to crush the uprising," said Omar Idilbi of the Local Coordination Committees group in Cairo. "Last month's acts of violence were unprecedented."
He said the increased use of the air force and artillery bombardments was behind the spike in casualties.
In Damascus, Syria state media said two bomb blasts at a Syrian army base injured four people.
The official Akhbariya channel showed images of blood-spattered rubble at the site, along with a battered black sport utility vehicle, and said "terrorists" had carried out the attack.
The blast took place in Abu Rummaneh, a well-guarded upscale area in central Damascus, where the ministry of defense and other government buildings are.
A truck bomb exploded in the same high-security zone on Aug. 15, injuring at least three people. Four senior government officials were killed in a bomb blast in Damascus on July 18.
Sunday's blasts came at the end of a bloody week during which Syrian armed forces ramped up security operations in and around Damascus, killing hundreds.
A spokesman for the Free Syrian Army said it had carried out the latest bombing as revenge for an attack by the military in the Damascus suburb of Darayya on Tuesday that killed at least 320 people.
The spokesman, who goes by the name Zain al Deen al Demashki, said rebels had bribed soldiers at the army facility to plant the explosives, which had been rigged with timed detonators. "We wanted to attack the regime in its own home," he said.
A major turning point in the civil war came last month when Assad's forces began widely using air power. The fighting also reached Syria's largest city, Aleppo, which had been relatively quiet for most of the uprising.
The Britain-based activist group Syrian Observatory for Human Rights said that 5,440 people, including 4,114 civilians, were killed in August. The Local Coordination Committees put the toll at 4,933 civilians.
The observatory and the LCC said more than 100 people were killed throughout Syria, and the groups have been reporting 100-250 deaths per day over the past week.
Syria's uprising has been the bloodiest in the Arab Spring that has removed authoritarian leaders in Egypt, Tunisia, Yemen, and Libya.
The two groups also released new death tolls for the entire uprising since March, 2011. The Observatory said more than 26,000 have been killed, including more than 18,500 civilians. The Local Coordination Committees put the death toll at more than 23,000 civilians. The LCC does not count members of the military who are killed, but the observatory does.
That averages out to about 1,300 to 1,500 deaths a month, making the August figure more than three times higher than average. The groups had reported a toll of about 20,000 more than a month ago.
On Thursday, Human Rights Watch said government forces have killed scores of civilians over three weeks by bombarding at least 10 areas near and around Aleppo where people were lined up to buy bread at bakeries.
Last week, activists reported that between 300 and 600 people were killed in the Damascus suburb of Daraya during days of shelling and a killing rampage by troops.
UNICEF spokesman Patrick McCormick said 1,600 were killed last week alone, including some children.
Meanwhile, on Sunday, the Observatory said the military pounded rebel holdouts in the Syrian commercial capital of Aleppo. There was also fighting in other areas, including the city of Homs, Idlib province on the border of Turkey and suburbs near Damascus.
The Observatory said 21 people were killed when troops stormed the village of Alfan in the central province of Hama. It added that eight people were killed in the province of Deir el-Zour, which borders Iraq.