Correspondents say the presence of the monitors has emboldened the protesters, despite further killings.
Up to 40 died on Thursday, activists said, mostly after security forces shot at crowds gathered in areas expecting a visit from the Arab team.
According to BBC News, at least 5,000 are believed to have died since the revolt began in March 2011.
The Arab League peace plan calls for a complete halt to the violence, the withdrawal of all armed forces and the release of all detainees.
According to Jim Muir of BBC News, Beirut, in many places the observers have found themselves surrounded by large crowds of demonstrators calling for the regime to go and for President Assad to be executed.
The presence of the monitors has encouraged protesters to come out on to the streets in bug numbers, and it has also emboldened them to take risks they might have shied away from before.
Shootings and deaths were reported from all the areas which the observers were visiting on their third day. The casualty figures put out by various activist coordination groups may be open to debate and cannot be independently confirmed, but they all suggest that the violence has got worse since the Arab observers began their mission on Tuesday.
The Arab mission has faced criticism for being led by Sudan's Gen. Mustafa al-Dabi, who Amnesty International has accused of carrying out human rights violations in his own country.
But the League says Gen. Dabi has full support, and the US has urged detractors to allow the team to finish its work.
Activists have called for massive protests on Friday - the traditional day of demonstration.
"On Friday we will march to the squares of freedom, bare-chested," the Syria Revolution 2011 Facebook group said, according to the Associated Press.
"We will march as we did in Homs and Hama where we carried olive branches only to be confronted by [President Bashar al-Assad's] gangs who struck us with artillery and machinegun fire."
Rami Abdul-Rahman, head of the Syrian Observatory for Human Rights, said the Arab League's initiative is "the only ray of light" there is for Syrians.
"The presence of the observers in Homs broke the barrier of fear," he said.
One activist in Hama told Reuters: "We know that just because they are here, it doesn't mean the bloodshed will stop. But at least they will see it."
Correspondents say that despite the presence of the Arab monitors - who are being escorted by state security officials - there has been little let-up in the ferocity of the response to protests.
At least 120 people have died since observers arrived in the country on Monday, according to activists.
The monitors have traveled to the central province of Homs, Idlib in the north, Deraa in the south, Hama and then the capital, Damascus.
On Thursday, the Syrian Observatory for Human Rights said at least four people were killed when security forces opened fire outside a mosque in Douma, a suburb of Damascus.
Monitors were arriving at the city hall there when security forces fired on "tens of thousands" of protesters outside the Grand Mosque, the UK-based group said.
It reported further deaths in other suburbs of the capital - Aarbin and Kiswah - as well as in Idlib and Hama. The US State Department said it was concerned by the continuing violence.
"We are concerned that even though we have monitors on the ground, and they are playing a role in some places, we also have the continuation of the violence," spokeswoman Victoria Nuland said.
Casualty figures and other information are hard to verify as most foreign media are barred from Syria.
The Arab mission is headed by Gen. Dabi, whose appointment has roused controversy due to his role as military intelligence chief in Sudan in the 1990s.
Gen. Dabi worked for Sudan's President Omar al-Bashir, who is wanted by the International Criminal Court (ICC) for his actions over Darfur.
One Arab League official in Cairo told AP that Gen. Dabi had the support of all its members, saying: "The mission and its final report will decide the future of Syria and this is not a small matter."
Source BBC News