Tens of thousands of protesters defied Syrian regime gunfire and took to the streets Friday, as state TV said the army foiled a would-be suicide attack a day after twin bombings in Damascus killed dozens.
At least 12 people died across Syria, including a guard gunned down after a large explosion outside Baath party offices in Aleppo on Friday evening, hours after the suicide bombing was reportedly thwarted in the northern city.
"The blast was powerful but we do not know what was the origin," said Rami Abdel Rahman of the Syrian Observatory for Human Rights. "We can confirm one death -- the guard of the Baath party office."
An opposition activist on the ground in Aleppo, Syria's second-largest city, told AFP the blast happened near a park which regime forces had emptied out of before it went off at around 8:45 pm (1845 GMT).
The activist, Mohammed al-Halabi, added however that there was a chance the explosion was caused by a sound bomb.
It came only hours after forces loyal to President Bashar al-Assad opened fire on protesters during a demonstration Aleppo, killing one civilian, said the Observatory.
Also on Friday, state television said the army foiled a would-be suicide attack in Aleppo by a bomber whose car was laden with 1,200 kilos (2,640 pounds) of explosives.
"The Syrian authorities have foiled an attempted suicide attack in Al-Shaar area in Aleppo, and killed the would-be attacker," the television channel said.
Anti-regime activists dismissed the official account of a foiled attack as "a lie," according to Halabi.
"It is not in the interests of the (rebel) Free Syrian Army to stage attacks on a Friday," the day of weekly mass anti-regime protests over the past 14 months, Halabi told AFP.
Traditionally a bastion of the Baath party, anti-regime sentiment has been on the rise in the commercial hub of Aleppo in recent months.
Syria's 14-month uprising began as a peaceful popular revolt but has turned into an insurgency amid mounting calls to arm rebels seeking to overthrow Assad, who heads the Baath party.
Elsewhere, civilians were killed in areas including central Hama and southern Daraa, where an 11-year-old child died from sniper fire, said the Observatory.
Troops shot and wounded five protesters in the capital and 20 in the central town of Helfaya, where two civilians also died, while another demonstrator was killed in Aleppo, it said.
Halabi said the Aleppo protester died from his wounds after regime forces opened fire in Salaheddine neighbourhood.
Speaking to AFP in Beirut via Skype, he said "thousands of people are protesting in spite of gunfire. They are condemning the criminality of yesterday's bombing."
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Demonstrators also condemned the United Nations for failing to stop the violence in Syria, calling for "immediate international military intervention," he added.
All but one of those killed on Friday were civilians, with one soldier killed and six others wounded in Jisr al-Shugur city in Idlib province when a blast hit their vehicle.
The violence came one day after two huge suicide blasts hit security premises in southern Damascus, causing devastation on an adjacent highway during rush-hour traffic.
At least 55 people died and 372 were hurt in the attacks, the deadliest since the start of the revolt in March 2011.
The attacks have raised fears that extremist elements could be taking advantage of the deadlock in Syria to stoke the unrest.
An Islamist group calling itself Al-Nusra Front claimed responsibility on the Internet for an earlier double bomb attack in Damascus, the SITE Monitoring Service said on Thursday.
It said two bombs it had placed near a military headquarters on a central highway in the capital on May 5 killed around 20 guards.
World powers condemned Thursday's attacks, which targeted a military intelligence building, and urged both sides to the conflict to adhere to the ceasefire brokered by UN-Aran League envoy Kofi Annan.
The Security Council urged the regime and rebels to "immediately and comprehensively" implement Annan's six-point peace plan, "in particular to cease all armed violence".
EU foreign policy chief Catherine Ashton also condemned attacks in the southern town of Deraa and in Damascus.
The Syrian government blamed foreign-backed "terrorists," a term used by authorities to refer to rebels seeking to topple Assad's regime.
The main opposition coalition, the Syrian National Council, responded by accusing the authorities of resorting to "terrorism" to bury the Annan plan.
In a televised speech, Lebanon's Hezbollah chief Hassan Nasrallah warned that Syria may descend into an Iraq-like abyss while accusing the US, Israel and some Arab states of stoking "terrorism" in the country.
"Who wants the destruction of Syria? America and Israel and some Arab countries," said Nasrallah, whose Shiite militant party is allied with the Damascus regime.
"They want to destroy Syria because it is the main ally of the resistance in Lebanon and Palestine."
More than 12,000 people, the majority of them civilians, have died since the uprising began, according to the Observatory, including more than 900 killed since the April 12 truce went into effect.