Demonstrators determined to show the strength of their movement to Arab League monitors deployed in hotspots across the country threw rocks at security forces in the Damascus suburb of Douma where troops tear-gassed the chanting crowds.
Five people were shot dead in the city of Hama and five in the city of Deraa in the south.
"Five were martyred today and at least 20 wounded when the Syrian security forces opened fire," the British-based Syrian Observatory for Human Rights reported, referring to Hama.
It said security forces fired at tens of thousands of protesters in the northern province of Idlib, wounding 25.
At least two dozen were injured in the Damascus suburb of Douma, activists said. One report said army defectors in Douma were engaged in armed clashes with troops. There were no further details.
Some 250,000 gathered after Friday's Muslim prayer in the northern province of Idlib at 74 different locations, according to the Observatory, an opposition network relaying activist reports.
"This Friday is different from any other Friday. It is a transformative step. People are eager to reach the monitors and tell them about their suffering," said activist Abu Hisham in Hama.
In Homs, the city at the centre of nine months of revolt, Al Jazeera television showed a huge crowd of dancing protesters who appeared to be in the thousands.
"Revolution, revolution Syria, revolution of glory and freedom Syria," they shouted.
In the Damascus suburb of Barzeh, where large crowds had also gathered, protesters held up signs saying "The Monitors are witnesses who don't see anything," and shouted, "Bashar we don't want you, Syrians raise your hands."
Activists in the city of Idlib said the army had put its heavy weapons out of sight.
"Security forces have moved some of their tanks out of the neighborhood streets and have put them behind buildings further out," said Manhal, a member of the local coordination committee. "They have also moved the tanks out of main streets. Some of them they moved into dugouts."
WITHDRAWAL OF FORCES
Assad has signed up to an Arab League plan for a verifiable withdrawal of his heavy weaponry and army from turbulent Syrian cities where more than 5,000 people have been killed since March, many shot during peaceful anti-government protests but also many killed in rebel attacks and defense actions.
The Arab League mission has met with strong skepticism from the outset, over its makeup, its small numbers, its reliance on Syrian government logistics and an initial assessment by its Sudanese chief that the situation was "reassuring."
That comment was met with disbelief in the West on Wednesday but on Friday, Syria's ally Russia accepted the judgment.
"Judging by the public statements made by the chief of the mission (Sudanese general Mustafa) al-Dabi, who in the first of his visits went to the city of Homs ... the situation seems to be reassuring," the Foreign Ministry said on its website.
However on Friday al-Dabi, whom some link to war crimes in Darfur in the 1990s, backed away from his comments. They were "unfounded and not true" a mission statement said, and all future statements would be in writing.
Activist video from Homs over the months has depicted a trail of death and destruction sowed by the military, with hundreds of killings of civilians reported.
"Unfortunately, reports show that the violence has continued in Syria over the past few days," Britain's Minister for the Middle East and North Africa, Alistair Burt, said.
"I urge the Syrian government to meet fully its obligations to the Arab League, including immediately ending the repression and withdrawing security forces from cities. The Syrian government must allow the Arab League mission independent and unrestricted access ..." Burt said.
In Brussels, a spokesperson for European Union foreign policy chief Catherine Ashton said the EU also "urges Syria to comply with the action plan of the Arab league in all its components" including "an immediate end of violence, the release of political prisoners, pulling the military out of cities."
PARTNER FOR PEACE?
The anti-government Free Syrian Army has ordered its fighters to stop offensive operations pending a meeting with Arab League delegates monitoring Assad's compliance with the peace plan, the rebels' commander said.
Colonel Riad al-Asaad said his forces had so far been unable to talk to the monitors, in the first week of their month-long mission, and he was still trying to contact them urgently.
"I issued an order to stop all operations from the day the committee entered Syria last Friday. All operations against the regime are to be stopped except in a situation of self defense," he told Reuters.
"We have tried to communicate with them and we requested a meeting with the team. So far there hasn't been any success. We haven't been given any of the (phone) numbers for the monitors, which we have requested. No one has contacted us either."
How widely Turkey-based al-Asaad's order is heeded by anti-government gunmen inside Syria is in question. A video shot by rebel fighters this week showed the ambush of a convoy of army buses in which, activists said, four soldiers were killed.
But the FSA, formed by thousands of defectors from Assad's military and security forces and financed by expatriate Syrians, has gone on the offensive in the past three months, taking the fight to the state rather than simply trying to defend opposition strongholds.
Its decisions are potentially crucial to any peace plan.
The Observatory for Human Rights said Syrian forces killed four people, including two defectors, in an ambush in Talkalakh near Lebanon's border.
The monitoring teams have encountered a range of problems, from hostility when they turn up under army escort, to random gunfire and communications breakdowns.
The mission has so far failed to end Syria's nine-month orgy of violence in response to demands for Assad to step down, although it was never advertised as a peacekeeping operation.
An Arab League member from a Gulf State played down expectations for the mission.
Even if its report turns out to be negative it would not "act as a bridge to foreign intervention" but simply indicate that "the Syrian government has not implemented the Arab initiative," the delegate told Reuters.
"The delegation is not meant to search or inspect anything other than this. It is not a fact-finding mission or an investigative committee ... The commission is meant to tell the League if Syria has committed to withdrawing its military from cities and to check if those who were detained during recent events have been released, and if Arab and international media are able to report on the situation freely or not."
Syria says it is fighting Islamist militants steered from abroad who have killed more than 2,000 of its security forces personnel. Activist sources do not dispute that there has been a significant toll among the security forces.
Most foreign journalists, including Reuters correspondents, are banned from the country, making it impossible to verify the reports on the ground.