Three years since the start of the uprising, nine million people have been displaced by fighting.
At least 17 people have been killed during fresh protests against the government in Syria, activists have said.
The reported deaths came after activists urged opponents of President Bashar al-Assad, emboldened by the presence of Arab League observers in the country, to take to the streets on Friday, a traditional day of mass protests.
Rights groups said dozens of civilians were killed as tens of thousands of people demonstrated a day earlier, as Arab League observers expanded their mission across the country.
“On Friday we will march to the squares of freedom, bare-chested,” the group Syria Revolution 2011 said on its Facebook page.
“We will march as we did in Homs and Hama where we carried olive branches only to be confronted by Bashar’s gangs who struck us with artillery and machine gun fire.”
On Thursday, Syrian activists called for the removal of the head of the Arab League monitoring team in a new blow to the credibility of the mission.
The opposition has condemned the observer’s presence as a farce to enable Assad to buy time and avoid more international censure and sanctions.
The 60 Arab League monitors are the first set of observers allowed in to the country during the nine-month uprising.
Their remit is to ensure that the government is complying with the terms of the League’s plan to end the crackdown on protests.
Syrian activists, however, doubt Arab monitors are getting the access they need to be able to give a fair assessment of the violence that the UN estimates has left more than 5,000 people.
They say the Arab team is only co-ordinating its work with the authorities and complain that security escorts, from the very forces that have sought to crush the protests, mean many activists dare not approach the monitors.
A member of the observer team told Al Jazeera the situation in Syria was “very dangerous”.
The official, who declined to be named, said there was constant shelling in the city of Homs with some areas under control of the Free Syrian Army, an umbrella group of armed anti-government fighters.
The source said he believed the Arab League mission was certainly going to fail.
The Syrian Local Co-ordination Committees, an umbrella group of anti-government activist organisations, put the death toll in Thursday’s violence at 38, many of them in cities that the Arab League delegation will tour.
The Syrian Observatory for Human Rights said most of those were killed when Assad’s forces opened fire on countrywide
protests. Six reportedly died in the central city of Hama, where monitors recently arrived.
The group said security forces fired on a protest in Douma, a Damascus suburb, and killed four people.
Enraged residents launched a civil disobedience campaign and thousands reportedly flooded the main square for a sit-in.
“The activists have called for complete civil disobedience. The roads have been blocked, stores are shut down and the city is paralysed,” said Rami Abdelrahman, head of the UK-based Observatory.
Monitors did not announce plans to inspect Douma on Thursday, but some residents said they saw cars with Arab League logos.
If true, it would be the team’s first surprise visit, but no residents have reported seeing or speaking to monitors.
‘Armed terrorist groups’
Speaking to Al Jazeera, Hadi Abdullah, an activist in Homs, said that monitors witnessed the crackdown on protests, but he was suspicious on how they would report it.
|Observers plan to visit protest hubs in the country|
“The observers saw a lot of violence in the city. They saw how security forces shoot at protests. They also saw the bodies of dead people,” Abdullah said.
“The monitors also saw destruction in the city. One of the observers asked residents of Baba Amr neighbourhood ‘How can you live in this place?'”
Another activist, Aram al-Dumi, from Douma, told Al Jazeera that there was a lack of co-ordination between activists and the observers.
“The delegation is relying solely on street signs when visiting the cities, they should rely on satellite images in order to locate the areas,” Dumi said.
“There has been reports of security forces changing the street signs, this has been the case in Douma, today we went to the grand mosque square after a funeral procession to demonstrate and greet the observers but the army fired at us.”
International diplomats from China, Russia and the US have urged Syria’s government to facilitate the observer mission.
The Arab League plan, endorsed by Syria on November 2, calls for the withdrawal of the military from towns and residential districts, a halt to violence against civilians and the release of detainees.
The Syrian government says most of the violence has been perpetrated by “armed terrorist groups” that are working against the government.