Amatuer video from Syria on Friday showed Arab League observers running from gunfire as security forces opened fire on civilians.
The film comes as tens of thousands took to the streets in continued protests against the regime of President Bashar al-Assad.
The Arab League mission to verify whether President Bashar al-Assad is keeping to a pledge to end the crackdown on a nine-month pro-democracy uprising has so far failed to bring a reduction in nine-months of ongoing violence.
Fresh doubts are also being raised about the credibility of the mission, with the head of the delegation suspected of committing war crimes in Sudan.
The head of the Syrian National Council, Dr Burhan Ghalioun, has called on the delegation to act to stop the killings rather than simply observe.
He said the Syrian government is holding more than 100,000 detainees, "some of them held in military barracks and aboard ships off the Syrian coast."
"There is real danger that the regime might kill them to say there are no prisoners," he warned
Friday's mass protests come after Syrian security forces shot dead 25 people on Thursday as they tried to disrupt protests in cities around the country - also wounding about 100 people.
Some 150 monitors in total are expected to enter Syria by the end of the week, but opposition leaders say people are being impeded from reaching them by security forces - a charged denied by Assad's regime.
"People really hope to reach the monitors. We do not have much access to the team. The people stopped believing anything or anyone now. Only God can help us now," on opposition leader said.
The United Nations says more than 5,000 civilians have been killed in the nine months of protests against Assad and the Arab League monitors are part of efforts to ease the bloodshed.
Assad’s government – which has found itself facing a growing deadly insurgency mounted by armed army defectors – claims 2,000 security personnel have also been killed.