Syrian government forces killed dozens of people in the northern city of Idlib, dumping their bodies in a mosque, while some 22 soldiers died in two separate rebel ambushes, opposition activists said on Tuesday.
The army intensified its assault on the Idlib province near the Turkish border, intermittently shelling built-up areas and spraying houses with machinegun fire in a bid to dislodge anti-government fighters.
Clashes were also reported in the eastern city of Deir al-Zor and security forces shelled Syria's third largest city, Homs, as the year-long uprising against President Bashar al-Assad's authoritarian rule increasingly resembles a civil war.
The United Nations says more than 8,000 people have died in the uprising and its refugee agency said on Tuesday that some 230,000 Syrians had fled their homes during the past 12 months, of whom around 30,000 have sought safety abroad.
In an apparent bid to deter the exodus, Syrian forces have laid landmines near its borders with Lebanon and Turkey, along routes used by refugees to escape the mayhem, advocacy group Human Rights Watch said.
Speaking after meeting opponents of Assad in Turkey, U.N.-Arab League envoy Kofi Annan said he was expecting to hear later on Tuesday the response from Syria to "concrete proposals" he had made to end the escalating violence.
By evening, there was no word on an answer, although the Syrian parliament said Assad had ordered a legislative election for May 7. It will be held under a new constitution, approved by a referendum last month which the opposition and their Western and Arab backers dismissed as a sham.
Both Russia and China have welcomed Assad's reform pledges, including the promised election, and have blocked moves in the United Nations to censure the Syrian leader.
But the U.S. State Department was dismissive of the plan: "Parliamentary elections for a rubber-stamp parliament in the middle of the kind of violence that we're seeing across the country? It's ridiculous," spokeswoman Victoria Nuland said.
Following a brutal crackdown in the central city of Homs, the army has intensified its operations in the north and has been shelling the town of Idlib for the past three days.
An activist in the town, speaking by telephone, said security forces had killed more than 20 people trying to leave the area in the past two days and dumped their bodies in al-Bilal mosque. When locals went to inspect the corpses, they too came under fire, pushing the death toll above 50, he said.
Another activist gave a slightly lower death toll.
"When people came from the neighborhood early this morning, the security forces also started firing at them. In total, about 45 people were massacred," said the man, who like many in Syria gave only his first name, Mohammed, for fear of reprisals.
Reports from Syria cannot be independently verified as the authorities deny access to rights groups and journalists.
Video footage showed the bodies of several unidentified men strewn on the floor of the mosque. An unseen voice said it was impossible to move them due to heavy shelling.
Army defectors killed at least 10 soldiers in an ambush in Idlib region, while rebels also killed 12 members of the security forces in the southern town of Deraa, according to the British-based Syrian Observatory for Human Rights.
Following meetings with Assad at the weekend in Damascus, former U.N. chief Annan held talks in Ankara with the Syrian National Council (SNC) - a fractious assortment of Assad opponents whose leadership lives abroad.
"I am expecting to hear from the Syrian authorities today, since I left some concrete proposals for them to consider," Annan told a subsequent news conference.
"Once I receive their answer we will know how to react."
Annan has not disclosed what his proposals entailed, but a diplomatic source said the U.N. envoy had told Assad he wanted an immediate cessation of hostilities, humanitarian access to the conflict zones and political dialogue.
SNC leader Burhan Ghalioun said the aim remained to secure a political and diplomatic solution, otherwise foreign governments would deliver on promises to supply weapons to rebel forces.
Sunni Muslim Saudi Arabia and Qatar have called for arms to be sent to help in the fight Assad, who is a member of the minority Alawite sect and is allied to Shi'ite Iran.
However, the SNC is deeply divided, as resignations from the council showed. Haitham al-Maleh, a former judge and veteran dissident, quit the SNC and another opposition leader, Kamal al-Labwani, said he too was preparing to resign.
"There is a lot of chaos in the group and not a lot of clarity over what they can accomplish right now," Maleh told Reuters in explaining his resignation from the SNC. "We have not gotten very far in working to arm the rebels."
Syria lies in a pivotal position, bordering Turkey, Jordan, Israel, Iraq and Lebanon. Its 23-million population comprises a mix of faiths, sects and ethnic groups, and analysts say the gathering conflict could destabilize the entire region.
While the rebels have only light weapons, the army has repeatedly used tanks, mortars and artillery.
"I have heard shelling in the Old City since 8 this morning," one activist in Homs told Reuters. "There is gunfire everywhere," he added, asking to be referred to only as Sami.
Human Rights Watch said anti-personnel and anti-vehicle mines of Russian origin had been found near Syria's borders, with indications they had been planted by the army this year.
Syria, like Russia, the United States and over 30 other states, has not signed up to a global ban on landmines.
"Any use of anti-personnel landmines is unconscionable," said Steve Goose, Arms Division director at HRW.
(Writing by Crispian Balmer; Editing by Alastair Macdonald)