Syria's main opposition group called on Thursday for an emergency UN meeting after the reported killing of more than 100 people in the city of Hama, as Russia blamed rebels of stoking the unrest.
The Syrian National Council appeal cast further doubt on a supposed UN-backed ceasefire that went into effect in the strife-torn country on April 12 but has failed to take hold amid persistent violence and killings.
"We are calling for an emergency meeting of the UN Security Council so that it can issue a resolution to protect civilians in Syria," an SNC statement said.
"Hama in recent days, and following a visit by UN observers, witnessed a series of crimes... that left more than 100 people dead and hundreds wounded because of heavy shelling."
Monitors said regime shelling of a working-class district of Hama killed at least 12 people on Wednesday and flattened a block of houses, but activists there put the death toll as high as 68, including 16 children.
State news agency SANA said 16 people were killed when a bomb that "terrorists" were preparing exploded prematurely inside a house in the central city.
At least 40 people were also reportedly killed in the city on Monday, including nine activists "summarily executed" after meeting UN monitors overseeing the ceasefire, according to a rights group.
The reports cannot be verified because of restrictions on foreign media.
Moscow, a long-time ally of Damascus, blamed the violence on rebel forces and hinted at Al-Qaeda involvement in the revolt against the regime of President Bashar al-Assad.
"Opposition groups have essentially reverted to waging wide-scale terror in the region," said Russian foreign ministry spokesman Alexander Lukashevich.
Attacks aimed at "killing as many peaceful civilians as possible and destroying civilian infrastructure remind one of what is happening in Iraq, Jordan and other places where Al-Qaeda and its groups operate," he said.
The truce brokered by UN-Arab League envoy Kofi Annan is to be monitored by 300 UN observers due to arrive in Syria in the coming weeks.
A small advance team is already on the ground, and some members have set up base in the flashpoint central city of Homs as well as in Hama.
The observers on Thursday inspected the site of the previous day's shelling in Hama, said Annan's spokesman Ahmed Fawzi, but there was no word on what they reported.
At least seven people were killed on Thursday, five of them civilians, according to the Syrian Observatory for Human Rights.
The Britain-based group said three died in gunfire by government forces in the northeast province of Deir Ezzor and two were killed near the northern city of Aleppo.
Damascus blamed the continued unrest on "armed terrorist groups" -- the term it uses for the rebels -- which it said had committed more than 1,300 violations since the truce came into force.
"Armed terrorist groups have intensified (the number of) massacres, explosions and acts of aggression, committing more than 1,300 violations since the ceasefire came into force on April 12," Information Minister Adnan Mahmoud told AFP.
In a sign of growing frustration with the Assad regime, Turkey said it was considering all possibilities if the unrest continues and the Council of Europe urged the Security Council to impose an arms embargo on Syria.
"In the face of developments in Syria, we are taking into consideration any kind of possibility in line with our national security and interests," Foreign Minister Ahmet Davutoglu told parliament during a briefing to lawmakers.
"Planning what kind of measures we will take if tens of thousands of people end up on our border is a requirement of being a big state," he said.
"This is not an intervention or warmongering as some claim."
France on Wednesday raised the prospect of military intervention in Syria if Annan's UN-backed peace plan fails.
Without quick progress, Foreign Minister Alain Juppe said the international community would have "to move on to another step which we have already started raising with our partners, under Chapter Seven of the United Nations charter."
A Chapter Seven resolution authorises foreign powers to take measures including military options.
Juppe added that such a resolution, which was also mooted by US Secretary of State Hillary Clinton last week, was unlikely to pass, alluding to previous Security Council vetoes by Russia and China.
The UN monitoring mission is doomed to fail because Assad will never comply with a ceasefire, top rebel military leader General Mustafa al-Sheikh was quoted as saying in pan-Arab daily Asharq al-Awsat on Thursday.
The Parliamentary Assembly of the Council of Europe on Thursday adopted a resolution condemning Assad's regime and urged the Security Council to urgently implement an embargo on sending weapons to Syria.
More than 9,000 people have died since the revolt erupted in March 2011, the United Nations says.