At least thirty people were killed Friday as Syrian troops intensified their crackdown on protesters, while explosions were reported near the Mazzeh military airport outside Damascus.
The violence followed Thursday's call by world leaders for President Bashar al-Assad to step down, dpa reported.
Syrian activists based at the Lebanese-Syrian borders said the death toll had risen to 30 after earlier reports of 22 dead.
"So far 30 people were killed ... and more than 200 were arrested, most of them are from the province of Daraa," an activist told the German Press Agency dpa shortly after midnight (2100).
Daraa is the flashpoint city of pro-democracy protests since the uprising in Syria started in mid-March. Activists dubbed the protests the "Friday of Signs of Victory."
They also quoted activists in the capital Damascus as saying that the situation "is very tense" in the Mazzeh district after four explosions were heard near Syria's Mazzeh military airport.
"The sound of four explosions was heard in the military airport and then heavy gunfire took place," activists told dpa.
The Mazzeh military airport is the headquarters of the Syrian fourth army unit.
"Unconfirmed reports are saying that a kind of mutiny inside the army unit has taken place, as some soldiers have refused orders to fire at protesters," a source added without elaborating.
Details of the violence in southern Daraa province were difficult to verify, as Syria has banned foreign media and international rights groupos from entering the country.
At least 16 of the dead were killed in southern Daraa province, including two teenagers, activists said.
"The protesters came under fire as they emerged from the mosque," Omar Idlibi, a Syrian activist based in Lebanon, told the German Press Agency dpa.
Ambulances were fired on as they tried to remove bodies, he said.
According to the online group, Local Coordination Committees of Syria (LCC), three of those killed in Daraa were soldiers who refused to open fire on protesters.
Others were killed in the central city of Homs and the Damascus suburb of Harasta.
An estimated 20,000 protesters took to the streets in the Khaldiya area of Homs.
In the coastal city of Latakia, security forces used loudspeakers to warn the residents of al-Gharraf and the vegetable market in the Raml area to remain indoors. They said anyone on the streets would be arrested.
In an interview with the French channel France 24, the United Nations chief human rights coordinator Navi Pillay said there was evidence of widespread human rights abuses committed by al-Assad's Syrian regime.
Pillay said the organization has compiled a list of 50 Syrians in senior positions that she said were responsible for violent repression.
"Atrocities are continuing. There continue to be violations," she said, citing "credible corroborated evidence" that regime forces have shot demonstrators and tortured prisoners - including young children.
The dead included two teenagers in southern Daraa province, including two teenagers, activists said.
In the coastal city of Latakia, security forces used loudspeakers to warn the residents of al-Gharraf and the vegetable market in the Raml area to remain indoors. They said anyone on the streets would be arrested.
At least 1,855 civilians and 422 security personnel have been killed since the protests calling for al-Assad's ouster started in Syria in mid-March, according to human rights advocates.
The reports are difficult to verify as the authorities have banned foreign media and international rights groups from entering the country.
Lebanese radio reported that more than 40 Syrian opposition groups had formed a coalition for a unified response to the regime of al-Assad.
Meanwhile, tens of thousands of people across the world launched an online campaign Friday on Twitter called "TellBashar2Go."
"If you TellBashar2Go, then you're telling the world that you support humanity's aspirations for dignity," posted Bint ElHara Layla on Twitter.
"Tell world leaders that their silence is louder than thunder," wrote another.
On Thursday, the United States, Germany, France, Britain and the European Union made the first direct call for al-Assad to step aside, citing the brutal crackdown on his own people and saying he had lost legitimacy to lead the country.
Later, the Syrian delegate to the United Nations, Bashar al-Jafaari, accused the Western nations of waging a "diplomatic war" against his country.
On Friday, EU countries decided to stop buying crude oil from Syria as they moved to toughen sanctions against al-Assad's regime, diplomats from the bloc said.
Syria is not a major oil power, having been projected by the International Monetary Fund to have produced less than 400,000 barrels per day last year. However, the sector was expected to provide about a quarter of government revenue.
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