DAMASCUS (AFP) ― 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 Nov. 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 U.N. 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.