|More than 1,200 people are said to have died in military action since anti-Assad protests first erupted in March [EPA]
The death toll in a government security crackdown in northern Syrian town has risen to 38, with 28 people dead on Sunday alone, according to the AFP news agency.
The operation is part of a crackdown that has been continuing since Saturday, when 10 people died, said a human rights group.
Rami Abdul-Rahman of the Syrian Observatory for Human Rights, a London-based independent rights group, said on Sunday that the deaths in the town of Jisr al-Shughour included six policemen. These figures have not been independently verified.
Security forces also shot dead two protesters in the eastern city of Deir Azzour on Sunday after mourners angered by the killing of a 14-year-old set fire to two Baath Party buildings, residents said.
Human rights groups say more than 1,200 people have died in the military action against anti-government protesters since March.
Bashar al-Assad, the Syrian president, has coupled military operations with symbolic overtures towards the opposition, including a general amnesty and a call for national dialogue.
Dialogue offer 'a joke'
At a meeting of Syria's mostly expatriate opposition in Brussels on Sunday, representatives said dialogue with the government would be "a joke" as long as the violent crackdown continued.
Obeda Nahas, one of the representatives chosen at a two-day Conference of the National Coalition to Support the Syrian Revolution, said any opposition figures who talked to the government right now would not be taken seriously by the Syrian people.
"We can't sit at the table and have some killers with us at the table," he said.
More shocking evidence of crackdown on protesters in Syria has appeared in video posted on YouTube
Nahas and other representatives renewed calls on foreign governments and the UN to increase political and legal pressure on Assad's government.
"We want more pressure on this regime because it doesn't seem to be listening to its own people," he said.
Ausama Monajed, another participant, said opposition figures were working to put together legal cases against the Assad government in federal courts in the US, several European courts and the International Criminal Court in The Hague.
Meanwhile, in Syria, Abdul-Rahman, of the Syrian Observatory for Human Rights, and other activists said, the military pulled back tanks from the outskirts of the central city of Hama and in southern villages.
A resident of the city, where at least 65 anti-government protesters were killed on Friday, said the tanks retreated from the outskirts of Hama overnight.
He said the situation in Hama remained "very tense". Residents were conducting a general strike in memory of children previously killed when security forces opened fire on anti-government protesters on Friday.
"Most of the shops here are closed, people are grieving and worried," he said by telephone on condition of anonymity for fear of reprisals.
The deaths in Hama and reports of tanks headed there had caused new alarm.
Activists on Sunday also said the army withdrew from the villages of Dael and Hirak near the city of Deraa where the uprising against the government began in mid-March.
The military had been conducting military operations in the area for days.
In-depth coverage of escalating violence across Syria
The Local Co-ordination Committees, which helps organise and document the protests calling for an end to the Assad government, said a total of 18 people died in Hirak and 12 in Dael since the start of the operations.
The activists reports could not be independently confirmed. The Syrian government has severely restricted the media and expelled foreign reporters, making it nearly impossible to independently verify events there.
Details of the operations in Jisr al-Shughour were also sketchy and attempts to reach residents of the town were unsuccessful, possibly because communications have been cut.
The state-run news agency, SANA, said on Sunday four policemen were killed and more than 20 wounded in the area when "armed terrorist" groups attacked government buildings and police stations.
It said the groups have been launching attacks against government buildings since Saturday, setting fire to a nmber of public and private buildings, cutting off roads and intimidating residents.