Last month was the deadliest in Syria since a revolt erupted in March last year, with about 1,000 people killed each week, the Syrian Observatory for Human Rights said on Saturday.
"In July, at least 4,239 people were killed across Syria," Rami Abdel Rahman, the director of the Britain-based watchdog, told AFP.
The figure includes 3,001 civilians -- among them civilians who have taken up arms -- as well as 1,133 government troops and 105 army defectors.
Violence has escalated dramatically in Syria as clashes have broken out in Damascus and the country's commercial capital Aleppo.
"The death toll is escalating," said Abdel Rahman, noting that in June, a total of 2,917 people were killed.
"June 2012 was the second-bloodiest month in the revolt," he said. "If we compare that with the 989 killed in the month following the start of the truce on April 12, we see that there has been a clear escalation in violence."
In total, at least 21,053 people died in violence across Syria since March last year, among them 14,710 civilians -- including those who joined the armed insurgency -- along with 5,363 troops and 980 defectors.
"The total number does not include the thousands of detainees whose fates we know nothing about," said Abdel Rahman. "Nor does it include those reported dead, but whose identities have been impossible to verify."
It is not possible to verify death tolls out of Syria, and the United Nations has stopped keeping a count of the victims.