The Local Coordination Committees sent Reuters a list with the names of 88 people, classified by region, the group said were killed in areas stretching from the port city of Latakia to Homs, Hama, Damascus and the southern village of Izra'a.
It was not possible to independently confirm the figures.
U.S. President Barack Obama condemned the violence and accused Assad of seeking help from Iran.
"This outrageous use of violence to quell protests must come to an end now," Obama said in a statement.
"Instead of listening to their own people, President Assad is blaming outsiders while seeking Iranian assistance in repressing Syria's citizens through the same brutal tactics that have been used by his Iranian allies."
That was an apparent reference to the suppression of anti-government protests in Iran, the biggest since the 1979 Islamic revolution, that erupted after a disputed 2009 presidential election.
Tens of thousands of people had taken to the streets of cities across Syria in the biggest demonstrations to sweep the country so far, and called for the "overthrow of the regime."
That reflected the hardening of demands which initially focused on reforms and greater freedoms.
The protests went ahead despite Assad's lifting of the state of emergency the day before. Ending the hated emergency rule, in place since the Baath Party seized power 48 years ago, was a central demand of demonstrators, who also seek the release of political prisoners and dismantling of the security services.
"This was the first test of the seriousness of authorities (toward reform) and they have failed," activist Ammar Qurabi said.
Washington urged Syria to stop the violence against protesters and British Foreign Secretary William Hague said emergency law should be "lifted in practice not just in word."
Friday's violence brings the death toll to about 300, according to rights activists, since the unrest which broke out on March 18 in the southern city of Deraa.
Activists cited the highest toll in the nearby village of Izra'a where protesters had been trying to head for Deraa. Residents said 14 people were killed.
"Izra'a is in the dark. No mobile phones or landlines working. People have been talking from villages near to Izra'a but not in the town," said Wissam Tarif of human rights organization, Insan.
Syrian television said eight people were killed and 28 wounded, including army personnel, in attacks by armed groups in the village. It added an armed group had attacked a military base in the Damascus suburb of Muadhamiya.
Amnesty International said it had been told of 75 deaths, including two children and a 70-year-old man.
Malcolm Smart, Amnesty International's Middle East and North Africa director, urged the authorities to stop the violence: "They must also immediately launch an independent investigation into what happened and ensure that any security forces found to have carried out these killings are brought to justice."
As in the Tunisian and Egyptian uprisings, citizens are rebelling against both a lack of freedom and opportunity and security forces' impunity and corruption that has enriched the elite while one-third of Syrians live below the poverty line.
In the first joint statement since the protests broke out, the activists coordinating the demonstrations Friday demanded the abolition of the Baath Party monopoly on power and the establishment of a democratic political system.
Aided by his family and a pervasive security apparatus, Assad, 45, has absolute power in Syria.
PROTESTS ACROSS COUNTRY
Protests swept the country of 20 million people, from the Mediterranean city of Banias to the eastern towns of Deir al-Zor and Qamishli. In Damascus, security forces fired teargas to disperse 2,000 protesters in the district of Midan.
In Hama, where Assad's father crushed an armed Islamist revolt in 1982, a witness said security forces opened fire to prevent protesters reaching the Baath Party headquarters.
"We saw two snipers on the building. None of us had weapons. There are casualties, possibly two dead," said the witness.
Syria's third city Homs, where security forces had killed 21 protesters this week when demonstrators tried to gather at a main square, was not spared Friday either.
"I was in the center of Homs and in front of me I heard a security commander telling his armed men: 'Don't spare them (protesters),'" rights campaigner Najati Tayara told Reuters.
Witnesses said security forces also shot at protesters in the Damascus district of Barzeh and the suburb of Douma.
Al Jazeera showed footage of three corpses, wrapped in white burial shrouds, which it said were from the eastern Damascus suburb of Zamalka.
Ahead of the main weekly prayers Friday, which have often turned out to be launch pads for major demonstrations, the army deployed in Homs and police put up checkpoints across Damascus, apparently trying to prevent protests sweeping in from suburbs.
After prayers finished in Deraa, several thousand protesters gathered chanting anti-Assad slogans. "The Syrian people will not be subjugated. Go away doctor (Assad). We will trample on you and your slaughterous regime," they shouted.
Assad's conciliatory move to lift the state of emergency followed a familiar pattern since the unrest began a month ago: pledges of reform are made before Friday when demonstrations are the strongest, usually followed by an intense crackdown.
Activists said some funerals for those killed Friday took place in Damascus suburbs in the evening. Funerals have been another platform for protesters in recent weeks and security forces have opened fire when mourners started demonstrating.
The authorities have blamed armed groups, infiltrators and Sunni Muslim militant organizations for provoking violence at demonstrations by firing on civilians and security forces.
Western and other Arab countries have mostly muted their criticism of the killings in Syria for fear of destabilizing the country, which plays a strategic role in many of the conflicts in the Middle East.