Syrian killings continue despite outside monitors.

It comes amid fresh reports of dozens of deaths as violence continues to sweep the country despite the presence of Arab League monitors.

Tens of thousands of protesters have taken to the streets in Syria, emboldened by the observers' mission but have come under continued attack by security forces. 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.

The Local Coordination Committee - the umbrella group for the activist network - has said it has documented the names of 130 people, including six children, who died since the Arab League monitors arrived in Syria on Monday night.

As news of the delegations movements spread, residents of towns and cities across the country came out in force, despite the crackdown.

"We know the observers won't do anything to help us," said Yahya Abdel Bari, an activist in the Damascus suburb of Douma. "But still, we want to show them our numbers, to let them know what is really happening here," he said.

Four protesters were killed and around 20 wounded when troops shot at a demonstration of 20,000 outside the city's Grand Mosque. "It came like rain, they used heavy machine guns, Kalashnikovs, everything," said Abdel Bari.

The Syrian Observatory for Human Rights said: "Syrian security forces opened fire on tens of thousands of demonstrators outside the Grand Mosque of Douma."

It added that the shooting happened when "Arab observers arrived at the city hall" as they continue to visit Syrian flashpoints. The inspectors began their mission to Syria on Tuesday in the city of Homs where activists say scores of protesters have been killed. There, they were greeted by angry crowds who feel the Arab League's presence is doing nothing to bring an end to the violence. They also spent two days visiting problem districts of Baba Amr, Bab Sbaa and Inshaat. Among the places they will now visit is Hama, which on Wednesday was the scene of more violence after tear gas was used at an anti-government rally.

Some of the observers will also travel south to the city of Deraa, another flashpoint for violent protests as well as Idlib province, where some 150,000 protesters took to the streets - more than on any other day recently, the Observatory said.

Before the latest deaths on Thursday, activists said at least six unarmed demonstrators had been killed this week. Pictures have emerged which seem to show Syrian security forces firing guns and tear gas at anti-government protestors in recent days. The clashes come as activists and human rights groups voiced concern over whether the Sudanese general leading the Arab League mission is an appropriate choice.

They claim his own defiance of a war crimes tribunal relating to Darfur means he may not display balanced judgement.

But the Arab League has said it is confident that the experience of General Mustafa al Dabi will enable him to assess the situation in Syria properly.

Gen Dabi, who is leading the 150-strong delegation to Syria, said: "Yesterday was quiet and there were no clashes.

"We did not see tanks but we did see some armoured vehicles. But remember, this was only the first day and it will need investigation.

"We have 20 people who will be there for a long time."

But Ausama Monajed, from the main opposition group Syrian National Council, said: "This (Arab League) mission has absolutely no mandate, no authority, no teeth.

"The regime does not feel obliged to even bring down the number of casualties a day," Sky News reported.