|President Bashar al-Assad has come under growing criticism over the crackdown on opposition protests [EPA]
Syrian security forces have opened fire at protesters in Deir ez-Zor, Idlib and Deraa after Friday prayers, according to media reports.
Al Arabiya television said on Friday there were also demonstrations in the central city of Homs and the western city of Latakia.
Earlier, Syrian security forces killed at least 11 people in raids near the Lebanon border and in the country's Sunni tribal heartland.
Rights activists also said forces shot dead a man and a woman as they pursued a crackdown on a protest ahead of Ramadan Friday prayers.
The man was killed early on Friday while trying to flee when security forces began arresting residents in the Damascus suburb of Saqba, Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, told the AFP news agency.
Nightly Ramadan prayers, or 'tarawih', which follow the breaking of the fast, have given more Syrians a focus for daily protest marches against 41 years of Bashar al-Assad family rule over the country of 20 million, activists said.
|Click here for more of Al Jazeera's coverage
Syrian authorities have expelled most independent journalists since the five-month-old uprising against the government of al-Assad began, making it difficult to verify reports from both sides.
The crackdown came a day after Hillary Clinton, the US secretary of state, urged nations around the world to step up pressure on al-Assad to curtail his government's brutal crackdown on protests.
In a televised interview on Thursday, Clinton suggested that China and India impose energy sanctions on Syria.
Clinton also urged Russia to stop selling arms to Damascus, which has bought arms from Moscow for decades.
She said in the interview with broadcasters that the US has been "very clear" in its statements about al-Assad's loss of legitimacy.
"But it's important that it's not just the American voice. And we want to make sure those voices are coming from around the world," Clinton said.
"What we really need to do to put the pressure on Assad is to sanction the oil and gas industry. And we want to see Europe take more steps in that direction.
"And we want China to take steps with us. We want to see India, because India and China have large energy investments inside of Syria. We want to see Russia cease selling arms to the Assad regime," the top US diplomat said.
Clinton's spokeswoman, Victoria Nuland, told reporters earlier that she did not know when Russia last made an arms delivery to Syria.
But when asked if Washington had asked Russia to stop arms sales, Nuland replied: "We have repeatedly, yes, and over many, many years and more than one administration."
Clinton, meanwhile, welcomed the fact that China and Russia, after refusing to condemn Syria, backed a UN Security Council statement last week denouncing the regime's crackdown.
Call for united opposition
Clinton added that an organised opposition was also needed to pressure al-Assad, adding that the US had been encouraging the opposition to unite.
"There are Syrian opposition figures outside of Syrian and inside," she said.
"But there's no address for the opposition. There is no place that any of us who wish to assist can go.
"There are many communities, minority communities within Syria who are frankly saying the devil we know is better than the devil we don't.
"So part of what we've been doing is to encourage the opposition to adopt a kind of unified agenda rooted in democratic change.
"So if you're a Christian, if you're a Kurd, if you're a Druze, if you're an Alawite, if you're a Sunni, inside Syria there'll be a place for you in the future."
Clinton's comments followed a visit by Turkey's foreign minister to Syria who held talks with officials on how to end the unrest. Turkey, Syria's powerful northern neighbour, and Arab nations have called for the attacks on civilians to stop.