Syrian pro-democracy activists plan to rally after midday prayers Friday against an Arab League observer mission they say will stall tougher action against the government over its opposition crackdown.
An Arab League advance team arrived in Syria Thursday to oversee a plan to end nine months of bloodshed as the opposition accused regime forces of "massacring" hundreds in two days.
But using the slogan "Protocol of death, a licence to kill", activists called on Facebook for nationwide protests against the mission.
Opposition leaders have charged that Syria's agreement to the mission was a mere "ploy" to head off a threat by the Arab League to go to the UN Security Council.
"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".
Even as the advance team arrived there was no let-up in the killing, with activists reporting at least 21 more people dead, and clashes between defectors and troops in the flashpoints of Homs and Idlib.
The observer mission is part of an Arab plan endorsed by Syria on November 2 that also calls for the withdrawal of the military from towns and residential districts, a halt to the violence and the release of detainees.
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.
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.
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.
The Enough Project, a non-governmental organisation, on Thursday condemned the fact that the mission is headed by a general it said was in charge of the Sudanese intelligence agency when "genocide" was committed in Darfur.
The opposition Syrian National Council charged Wednesday that regime forces had killed 250 people in 48 hours in the run-up to the advance team's arrival.
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The Syrian Observatory for Human Rights released a grisly video to back its claim that security forces committed a massacre 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 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.
On Thursday, nine people were killed 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, and there were clashes 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, the 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.
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.
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.
There were tensions at the meeting, however, with Russia renewing demands for an inquiry into NATO airstrikes in Libya in a move US ambassador Susan Rice called "a cheap stunt" to divert attention from the Syria crisis.
Russia and China have already vetoed one resolution proposed by European countries condemning Syria. Russia, which accuses the West of seeking regime change in Syria, last week proposed a new text that the European countries say is not tough enough on President Bashar al-Assad.
State news agency SANA claimed Thursday more than 2,000 members of the security forces had been killed since anti-government protests erupted in March.