Of the 15,804 people killed since March last year, almost 5000 had died since a UN-backed ceasefire was supposed to take effect on April 12, says UK group
Close to 16,000 people have been killed since the outbreak of the Syrian revolt 15 months ago, a human rights watchdog says.
And the past seven days have been the bloodiest so far with 916 deaths.
"The pace of the killings has escalated," the Britain-based Syrian Observatory for Human Rights said on Wednesday.
"The last week was the bloodiest week of the Syrian Revolution," Observatory director Rami Abdel Rahman told AFP by telephone. He said 916 people had been killed from June 20 to 26.
Of the 15,804 people killed since March last year, 4,681 had lost their lives since a UN-backed ceasefire was supposed to take effect on April 12, he said.
Of those, roughly a quarter - 1,197 - had been killed since the UN observer mission intended to oversee the peace plan suspended its operations on June 16 in the face of the mounting violence.
"The last month, from May 26 to June 26, was the deadliest since the start of the protests. During this period, 3,426 people were killed," Abdel Rahman said.
The statistics were released after 129 people were killed in violence on Tuesday, 79 of them civilians, according to the Observatory's figures.
The UN's deputy envoy for Syria, Jean-Marie Guehenno, told the UN Human Rights Council on Wednesday that the violence in Syria had "reached or even surpassed" levels seen before the ceasefire agreement and that a six-point peace plan forged by his boss, UN-Arab League envoy Kofi Annan, "is clearly not being implemented".
Senior diplomats said world powers would meet on Saturday in an attempt to end the bloodshed.
US Secretary of State Hillary Clinton and Russian Foreign Minister Sergey Lavrov would be joined by other top diplomats from UN Security Council nations and possibly neighbours of Syria.
Meanwhile, a report on UN probe into a massacre in the central Syrian village of Houla has concluded that forces loyal to the government "may have been responsible" for many of the deaths.
The report released to the UN Human Rights Council in Geneva by UN-appointed human rights experts said most of the victims were women and children who were slaughtered in their homes.
The findings of the report triggered a walkout by the Syrian delegation as it was being read out.
"We will not participate in this flagrantly political meeting," said Syrian ambassador Faisal Khabbaz Hamoui before leaving the hall.
The walkout came as the commission told the council that the unrest was taking on an increasingly sectarian basis.
"Where previously victims were targeted on the basis of their being pro or anti-government, a growing number of victims appear to have been targeted because of their religious affiliation," said the report.
It said: "Gross violations of human rights are occurring regularly, in the context of increasingly militarised fighting."
