Away from the battlegrounds, efforts to find a viable political alternative to Assad's rule faltered when an exiled umbrella opposition group said it would boycott Arab-brokered talks to unite its splintered ranks.
The latest bloodshed centred in Rastan, where opposition sources said rebels killed 23 members of Assad's security forces in fighting while heavy government shelling of the town killed nine people - further unravelling an April 12 ceasefire deal that is being overseen by international monitors.
Rastan, 180 km (110 miles) north of Damascus, has slipped in and out of government control during a 14-month-old uprising in which peaceful protest has given way to a sectarian-tinged insurgency that answers Assad's violent bid to crush unrest.
"Shells and rockets have been hitting the town since three a.m. (midnight GMT) at a rate of one a minute. Rastan has been destroyed," a member of the rebel Free Syrian Army (FSA) in Rastan who declined to be named told Reuters by satellite phone.
He said that among those killed was Ahmad Ayoub, an FSA commander whose fighters were battling army forces he said were comprised of elite units and members of Military Intelligence.
The Britain-based Syrian Observatory for Human Rights said rebels destroyed three armoured personnel carriers and seized two others, capturing around 15 soldiers.
Syria's state news agency said "terrorists" assassinated a military officer in Damascus and an intelligence officer in Deraa, where the uprising against Assad first took shape.
Saudi Foreign Minister Saud al-Faisal, who has previously called for arming the rebels, said on Monday that special U.N.-Arab League envoy Kofi Annan's peace plan was losing meaning as bloodshed was raging on.
"Confidence in the efforts of the envoy of the United Nations and the Arab League has started to decrease quickly," he told a news conference in the Saudi capital Riyadh.
SANA, the Syrian official news agency, also said Abdelaziz al-Hafl, a pro-Assad tribal notable in the oil-producing province of Deir al-Zor, was slain on Monday along with his son.
Opposition sources said Hafl was the 17th prominent Assad supporter killed in the eastern province in recent months.
A member of Hafl's tribe said he had been repeatedly warned by insurgents to stop cooperating with the secret police, "but he did not heed the warnings and was bumped off today".
There was no independent confirmation of any of the reports of fighting and killing from inside Syria, which has severely limited media access over the course of the uprising.
Syria's Sunni Muslim majority is at the forefront of the revolt against the authoritarian Assad, whose minority Alawite sect is an offshoot of Shi'ite Islam. Assad's government says it is fighting a terrorist attempt to divide Syria.
The exile group that claims the right to speak for the political opposition to Assad, the Syrian National Council (SNC), said it would not join Arab League-brokered talks set for Wednesday and Thursday aimed at healing its divisions.
"The SNC will not be going to the meeting in Cairo because it (the Arab League) has not invited the group as an official body but as individual members," Ahmed Ramadan told Reuters in Rome, where the group is trying to decide its leadership.
In a statement, the group rejected talks it said were aimed at negotiations with Assad, who it said must quit power: "No negotiations can be held properly unless their aim is the end of the dictatorship and moving the country to democratic rule."
Political jockeying within the SNC has prevented it from gaining full international recognition as the sole representative of the anti-Assad movement. Executive members told Reuters they may choose a new president or restructure the council in a bid to garner broader support.
The United States, Europe and Gulf Arab states want Assad to step down but his ally Russia has blocked more robust action against Syria in the U.N. Security Council while backing Annan's peace blueprint.
Deputy Foreign Minister Gennady Gatilov defended Russia's weapons deliveries to Syria in the face of Western criticism, saying government forces need to defend themselves against rebels receiving arms from abroad.
In Brussels, the European Union said in a statement that it had extended sanctions against Syria, freezing the assets of two companies it said gave financial support to Assad's government, and imposing travel bans on three people.
But Western powers have shown no appetite to repeat the military intervention that helped Libyan rebels topple dictator Muammar Gaddafi last year, and Moscow says arming Assad's opponents would only lead to years of inconclusive bloodletting.
U.N. Secretary General Ban Ki-moon said last week there was only a narrow window of opportunity to avert full-scale civil war in Syria, which straddles a crossroads of Middle East conflict bordering Turkey, Jordan, Israel, Iraq and Lebanon.
Syria's 23-million population comprises a mix of sects and ethnic groups whose tensions resonate in neighbouring countries.
Those tensions have flared in the last two days in the Lebanese port city of Tripoli, where medical sources said on Monday that running battles between Alawite supporters of Assad and Sunni fighters left at least five dead and 70 wounded.
Tension in Tripoli had been on the rise since last week when Sunni Islamists - broadly sympathetic to Syria's rebels and at times supporting them logistically - held a sit-in to protest the arrest of a man who Lebanese authorities said had been in contact with an unnamed "terrorist organisation".
Judicial sources in Lebanon - where Syria has sway over the intelligence and security organs dating to the Lebanese civil war and its aftermath - said on Wednesday that Shadi al-Moulawi had been charged with belonging to an armed "terrorist" group.