The presence of Arab League monitors in Syria has re-energized the anti-government protest movement, with tens of thousands turning out over the past three days in cities and neighborhoods where the observers are expected to visit.
The huge rallies have been met by lethal gunfire from security forces.
Thursday, security forces opened fire on tens of thousands protesting outside a mosque in a Damascus suburb and killed at least four. The crowd had gathered at the mosque near to a municipal building where the monitors' cars had been spotted.
Troops fired live ammunition and tear gas to disperse large protests in several areas of the country, including central Damascus, killing at least 26 people nationwide, activists said.
A key activist network, the Local Coordination Committees, said it has documented the names of 130 people, including six children, who died have since the Arab League monitors arrived in Syria Monday night.
The ongoing violence, and new questions about the head of the Arab League monitors, a Sudanese general who held key security positions in the regime of President Omar al-Bashir accused of committing genocide in Darfur, are reinforcing the opposition's view that Syria's limited cooperation with the observers is nothing more than a farce for President Bashar Assad's regime to buy time and forestall more international condemnation and sanctions.
Still, the presence of outside monitors has invigorated frustrated protesters and motivated them to take to the streets again in large numbers after months of demonstrations met by bullets had dashed their hopes of peaceful change.
"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."
The 60 Arab League monitors, who began work Tuesday, are the first Syria has allowed in during the nine-month anti-government uprising. They are supposed to ensure the regime complies with terms of the Arab League plan to end Assad's crackdown on dissent. The U.N. says more than 5,000 people have died in the uprising since March.
The plan, which Syria agreed to on Dec. 19, demands that the government remove its security forces and heavy weapons from cities, start talks with the opposition and allow human rights workers and journalists into the country. It also calls for the release of all political prisoners.
As word spread Thursday morning that the observers would be visiting Douma, thousands of people began gathering outside the Grand Mosque, calling for Assad's downfall and for international protection for civilians.
Amateur videos posted on the Internet showed protesters in Douma facing off with Syrian soldiers, shouting "Freedom, Freedom!" Troops then opened fire to disperse the roughly 20,000 protesters.
Rami Abdul-Rahman, head of the British-based Syrian Observatory for Human Rights, said cars belonging to the Arab League monitors were seen in front of a municipal building close to the mosque around the same time.
But after the killings, he said monitors were barred by security officials from entering Douma and the situation quickly deteriorated. A witness said angry citizens closed off streets with rocks and garbage containers, and thousands of people returned to the area around the Grand Mosque to stage a sit-in.
Troops also surrounded a mosque in Damascus' central neighborhood of Midan and tossed tear gas canisters at hundreds of people calling for the downfall of the regime.
In the northern Idlib province, about 150,000 protesters took to the streets -- more than on any other day recently, the Observatory said.