BEIRUT: Rebels and regime troops clashed in a district of the Syrian capital as scores of protests were held across the strife-torn country and more than 20 people killed on Friday, monitors said.

Clashes broke out in Kfar Sousa, a Damascus district where anti-regime sentiment is strong, while explosions rocked the Mazzeh and al Qaeda neighbourhoods, according to the Syrian Observatory for Human Rights.

Protesters, meanwhile, took to the streets in flashpoints across the country, including Damascus and the northern city of Aleppo, where regime forces used live rounds and tear gas, the NGO added.

Anti-regime activists had called for fresh protests under the slogan “Revolutionaries and traders, hand in hand until victory,” aiming to draw in the middle classes in Syria's two largest cities to join the uprising.

“Damascus and Aleppo play a central role in the revolt now,” anti-regime activist Deeb Dimashqi (not his real name) told AFP via Skype.

People emerged from mosques to demonstrate in Kfar Zita, in Hama province of central Syria, chanting: “We don't want peaceful (revolt). We have bullets and Kalashnikovs!””Meetings, decisions, sanctions...initiatives, and still the Syrian people is being slaughtered,” read a hand-written poster held up by a Kfar Zita protester, according to amateur video posted on YouTube by activists.

Amid the protests, violence continued across the country.

The rebel district of Khaldiyeh, in the restive city of Homs, underwent “the most violent shelling it has seen since the revolt began” in March 2011, said the Observatory, “at a rate of five shells a minute.”According to video uploaded on YouTube by anti-regime activists, thick clouds of smoke rose above residential buildings and mosques in Khaldiyeh, where loud blasts were heard as the district, much of it deserted, was violently shelled.

The opposition Syrian National Council in a statement called on UN military observers to set up a base in the city, “which suffers daily shelling and killings by regime snipers.” The Observatory said a man was killed in the province of Homs when unidentified gunmen opened fire on a small convoy of vehicles.

An explosion in front of a police station in the northwestern city of Idlib killed five people, including two more members of the security forces, said the Britain-based monitoring group.

“It was a powerful explosion that destroyed the facade of the building,”said the watchdog, which also reported that a civilian was shot dead at Kfar Nabel in the same province.

A deadly blast also rocked a Damascus suburb, killing two security forces members, said the Observatory.

An AFP photographer said the blast in the capital's Qudssaya neighbourhood tore a car to shreds and damaged a military bus — the reported target — as well as some nearby residential buildings.

Four others were killed in the suburbs of Damascus, one of whom was shot dead by a sniper in the town of Douma, the watchdog said.

In the southern province of Daraa, cradle of the uprising, the head of a rebel “brigade” was killed at Basr al-Sham and a sniper shot dead a civilian in Mahajja, said the Observatory.

In Latakia on the Mediterranean, two rebel fighters were killed in clashes in Al-Hafa, a mountainous area where “regime troops have lost dozens of soldiers over the past 72 hours,” the Observatory said.

In Deir Ezzor, eastern Syria, three civilians were killed in shelling at dawn, while two regime troops were killed in clashes.