Updated 5:37 AM EDT, Mon April 22, 2013
The bodies of at least 566 people who were killed over a six-day period across Syria were found Sunday, according to Local Coordination Committees in Syria, an opposition group based in the country.
That is the highest number of victims discovered in a single day since the war began in March 2011, LCC spokeswoman Rafif Jouejati said.
At least 450 bodies were found in the Damascus suburb of Jadidat al-Fadel, LCC activist Abu Aasy said Sunday.
Over the past six days, some 3,000 members of the security forces stormed the area, the activist said. He said the dead include at least 300 civilians and 150 members of the rebel Free Syrian Army.
"The Local Coordination Committees in Syria extends its deepest condolences to the families of the martyrs of our revolution for freedom and dignity in general," the group said in a statement.
"The LCC holds the Syrian regime fully responsible for the brutal crimes committed against unarmed civilians, and calls on the United Nations Security Council to refer these crimes to the International Criminal Court as war crimes."
The Syrian government, meanwhile, said armed forces "inflicted heavy losses upon terrorists in the town of Jdiadet al-Fadl in Damascus Countryside, injuring a number of them (and) killing others," the state-run Syrian Arab News Agency reported.
The war in Syria has raged ever since protesters, partly inspired by Arab Spring uprisings in the region, began demonstrating for more freedom two years ago.
That movement quickly morphed into a movement against President Bashar al-Assad, who was appointed president by Syria's parliament in 2000 after his father died. The government responded to the demonstrations with a brutal crackdown.
In February, the United Nations estimated that 70,000 people had been killed in the fighting.
CNN cannot independently verify death tolls or other accounts of violence in Syria as the government severely restricts access by international journalists.