US President Barack Obama demanded Damascus "immediately" halt its crackdown on protesters, as activists said Syrian troops killed at least three people in raids on Latakia and other towns.
Obama and Saudi King Abdullah in a telephone call expressed their "shared, deep concerns about the Syrian government's use of violence against its citizens," the White House said.
"They agreed that the Syrian regime's brutal campaign of violence against the Syrian people must end immediately."
The call came after Saudi Arabia, a Sunni Muslim regional heavyweight which had remained silent on the five-month revolt, added its voice to a chorus of criticism and recalled its ambassador from Damascus.
In a separate phone call, Obama and British Prime Minister David Cameron also agreed on the need for an "immediate" end to the bloodshed.
They reiterated "their deep concern about the Syrian government's use of violence against civilians and their belief that the Syrian people's legitimate demands for a transition to democracy should be met."
The Syrian Observatory for Human Rights said two people were killed and 15 wounded, four of them critically, during a military operation in the southern Latakia area of Ramleh, a nerve centre of anti-regime protests.
It said military vehicles, including tanks and armoured personnel carriers, converged on Ramleh, sparking an exodus of residents.
Security forces raided the city's Asaliba district, arresting "more than 70 people" in a door-to-door crackdown, it said, adding that women who resisted the arrest of their children were harassed and beaten.
An activist in the Homs region of central Syria said troops backed by two tanks also entered the village of Jussiyeh which borders Lebanon, triggering a stampede across the frontier and to neighbouring areas.
Military vehicles, meanwhile, swooped on the town of Qusayr, likewise in Homs province, where security and intelligence services carried out arrests and killed one person, the Observatory said.
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In Huleh, another town in Homs province, families received the corpses of four relatives who had been arrested in the past few days, the Observatory said.
Security forces backed by tanks have been trying to crush dissent city by city and town by town since pro-democracy protests erupted in mid-March.
The Observatory says 2,150 people have been confirmed dead since then -- 1,744 civilians and 406 members of the security forces.
Activists said at least 20 people were killed on Friday when security forces opened fire on thousands of anti-regime protesters who rallied in flashpoint cities after Muslim weekly prayers, updating earlier tolls.
State television, meanwhile, said "two security agents were shot dead by armed men in Douma," a suburb of the capital.
Organisation of Islamic Cooperation (OIC) chief Ekmeleddin Ihsanoglu on Saturday urged "the Syrian leadership to exercise utmost restraint through immediate cessation of the use of force to suppress people's demonstrations."
Ihsanoglu "expressed the readiness of the Organisation of Islamic Cooperation to play a role in this regard, as he believes that dialogue is the only secure option through which this devastating crisis could be contained."
Canada also bolstered sanctions, freezing the assets of more senior officials, and companies linked to the Damascus regime.
The UN Security Council is to hold a special meeting next Thursday to discuss human rights and the humanitarian emergency in Syria, diplomats at the United Nations said.
In a Twitter statement, France's UN mission said UN Human Rights Commissioner Navi Pillay and UN under-secretary for humanitarian affairs Valerie Amos were to brief the meeting.
As the West grapples with ways to pressure Damascus into ending the bloodshed, US Secretary of State Hillary Clinton has urged countries to stop trading with Syria.
"We urge those countries still buying Syrian oil and gas, those countries still sending Assad weapons... to get on the right side of history," Clinton told reporters.
France on Saturday followed the example of the United States in advising its citizens in Syria to leave the country.