An Arab League advance team arrived in Syria on Thursday to launch a hard-won observer mission to oversee a plan to end nine months of bloodshed after the opposition accused regime forces of "massacring" hundreds in two days.
Meanwhile, there was no let-up in the killing, with human rights activists reporting at least 21 more people killed and clashes between defectors and regular troops in flashpoints Homs and Idlib.
The Arab League team "arrived in the afternoon and then left to attend a meeting," a hotel spokesman said.
It is part of an Arab plan endorsed by Syria on November 2, which also calls for the withdrawal of the military from towns and residential districts, a halt to the violence and the release of detainees.
Opposition leaders have charged that Syria's agreement to the mission on Monday was a mere "ploy" to head off a threat by the Arab League to go the UN Security Council.
The opposition Syrian National Council charged on Wednesday that regime forces had killed 250 people in 48 hours in the run-up to the advance team's arrival.
The Syrian Observatory for Human Rights released a grisly video to back its claim that security forces committed a massacre on Tuesday in the town of Kafer Awid in northwestern province of Idlib.
The video zooms in on the faces of at least 49 men, some of them completely disfigured, before panning out to what appear to be rows of additional corpses.
In Berlin, the foreign ministry said it had summoned Syria's ambassador to demand an immediate halt to the "brutal" repression of anti-regime demonstrators.
"The brutal acts by the security forces against the Syrian population are absolutely unacceptable and a flagrant violation of Syria's agreement with the Arab League," said Boris Ruge, the ministry's head of Middle East affairs.
"Given the crimes that have come out into the open, everyone should be asking himself if he can morally serve such a regime," he said in a statement.
On Thursday, nine people died in the central city of Homs, the Syrian Observatory for Human Rights said, adding the number could rise given the "high number of wounded in critical condition."
In Idlib, security force gunfire killed four civilians, the Observatory said, with clashes underway between security forces and defectors in the town of Kharbet-Ghazale.
An attack carried out by defectors in retaliation for the previous day's killing of eight civilians, including a 10-year-old child, left one soldier and eight others wounded in the same province.
Further south in Daraa, cradle of the uprising, "a civilian was killed in the town of Tafas during raids by security forces searching for activists."
Elsewhere, four soldiers and two defectors, were killed in clashes in a checkpoint in Baba Amro.
Pro-democracy activists called on Facebook for nationwide protests on Friday against the observer mission, with the slogan "Protocol of death, a licence to kill."
The advance team consists of a dozen security, legal and administrative staff from the Arab League's secretariat, who will make the logistical preparations for the arrival on Sunday of an initial 30 observers.
"Their mission is to consult with Syrian officials to prepare for the delegation's visit," Arab League secretary general Nabil al-Arabi said.
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The mission's leader, veteran Sudanese military intelligence officer General Mohammed Ahmed Mustafa al-Dabi, said its numbers would swell to a total of between 150 and 200 in the following days.
According to their marching orders, they will number an "amount reasonable to accomplish the mission" and will include "Arab civilian and military experts chosen by Arab countries or organisations."
Their task will be to monitor the "cessation of violence on all sides, and to ensure the release of detainees arrested in connection with the current crisis," according to the text of the protocol.
Observers "should be free to communicate with anyone, in coordination with the Syrian government."
Foreign ministry spokesman Jihad Makdisi said it was "honest and important" that the text of the protocol referred to violence on all sides as well as armed groups, "because it takes into account armed gangs."
Foreign Minister Walid Muallem has said he expects the observers to vindicate Damascus's claims that the unrest has been caused by "armed terrorist groups," not peaceful protesters as maintained by Western governments and human rights watchdogs.
Muallem has said the observers will be able to access so-called "hot zones" but not sensitive military sites. Human Rights Watch called on Damascus to grant full access.
Syrian opposition groups have criticised the observer mission.
"We call on the Arab League to refer the matter of the crisis in Syria to the UN Security Council," said Omar Edelbi, spokesman for the Local Coordination Committees, which have been driving the protests on the ground.
He called the observer mission "another attempt by the regime to bypass the Arab initiative and empty it of its contents."
The United Nations estimates that more than 5,000 people have been killed in the regime's crackdown since mid-March.
In New York, France said "significant progress" had been made at a UN Security Council meeting on Syria.
"We are waiting for Russia to do all it can for negotiations to proceed rapidly" on a resolution it proposed condemning the violence in Syria.
For its part, state news agency SANA said Thursday more than 2,000 members of the security forces had been killed since anti-government protests erupted in March.
"In response to a fallacious (UN) report on the situation in Syria, we have informed the office of the UN High Commissioner for Human Rights that the number of martyrs has surpassed 2,000 members of the security forces and the army," according to a letter SANA says was sent.
At the same time, Damascus denounced "politically motivated, false reports of the UN High Commissioner for Human Rights and the international commission established by the Human Rights Council," SANA said.
On December 2, the rights council urged tougher international action against Syria, condemning "gross violations" of human rights following evidence security forces killed and tortured dissidents.
Syria insists that there are "hundreds of terrorists who have publicly admitted killing protesters, committed robberies and assassinations and disseminated fabricated information in exchange for money provided from neighbouring countries."
It accused the commission of being "in step with the plans of certain countries who want to destroy Syria and impose a military intervention ... while serious crimes are committed by terrorist groups."