Syria 'massacre': Opposition calls for UN action
Syria's main opposition coalition has called for emergency meetings of the UN Security Council and the Arab League to discuss the intensifying violence in the north-west of the country.
The Syrian National Council, which is based outside Syria, says about 250 people have been killed since Monday.
A human rights group has accused the Syrian authorities of carrying out an "organised massacre" in Idlib province.
Arab League monitors are due in Syria on Thursday under a peace initiative.
UN Secretary General Ban Ki-moon was "extremely concerned about the escalating crisis and the mounting death toll in Syria", his spokesman said.
He urged the government of Syrian President Bashar al-Assad to give its "full co-operation" to the Arab League plan.
Washington said it was "deeply disturbed" by the reports of escalating violence.
White House spokesman Jay Carney said the Assad regime had "flagrantly violated" its earlier pledges to end violence.
'Protected zone' plea
The latest wave of violence is taking place in the Jabal al-Zawiya area, not far from the border with Turkey.
The Syrian Observatory for Human Rights, based in London, said that on Tuesday security forces killed more than 110 people, most of them army defectors, around the village of Kansafra.
The previous day, up to 70 defectors were shot dead when they attempted to flee a nearby base, it added.
The Observatory also said that on Wednesday, at least 22 people - six army deserters, a civilian and 15 members of government forces - were killed in clashes in the southern Deraa province.
Another activist organisation, the Local Co-ordination Committees, said 15 people had been killed so far on Wednesday, in Hama, Idlib, Homs and Deraa.
Journalists are not allowed to report freely in Syria so details are hard to verify.
The Syrian National Council (SNC), which is the main opposition umbrella group, said on Wednesday that it wanted the UN Security Council to declare a "protected zone" in the areas under attack by the army.
It also urged both the Security Council and the Arab League to act to protect people in those areas.
France, which is a permanent member of the Security Council, has backed the call for action.
"There was a massacre of an unprecedented scale in Syria on Tuesday," said French foreign ministry spokesman Bernard Valero.
"It is urgent that the UN Security Council issues a firm resolution that calls for an end to the repression."
The fighting involves armed opposition groups, made up largely of army defectors, who have been taking on the Syrian security forces.
Reports from Idlib province suggest that army reinforcements are arriving and that clashes are continuing, with the number of casualties rising.
The BBC's Jim Muir, who is monitoring events from neighbouring Lebanon, says it may be no coincidence that the surge in violence comes ahead of the arrival of Arab League monitors.
He says the Syrian authorities might be "clearing up unfinished business" ahead of the arrival of the monitors, with reports suggesting the security services are acting against army deserters and civilians trapped in a valley.
Our correspondent says opposition fighters may be trying to establish their presence to gain a foothold for further expansion.
Damascus says it is fighting "armed terrorist gangs" who want to destabilise the country.
Iran said on Wednesday that five Iranian technicians working on a power plant near the Syrian city of Homs had been abducted by an unidentified group, the Mehr news agency reported.
The Iranian embassy in Damascus called for their immediate release.
Syria's state news agency, SANA, says eight engineers from different countries disappeared while travelling by bus to the power plant.
The UN said earlier this month that more than 5,000 people had been killed across Syria since protests against President Bashar al-Assad erupted in March.
The announcement that Damascus had agreed to the Arab League observer mission was made on Monday.
Syrian Foreign Minister Walid Muallem said the country's sovereignty would be protected because the Arab League had agreed to amendments to the deal, which also calls for all violence to be halted, for the withdrawal of troops from the streets and the release of detainees.
The observers would be "free" in their movements and "under the protection of the Syrian government", Mr Muallem added, but would not be allowed to visit sensitive military sites.
The observers will have a one-month mandate that can be extended by another month if both sides agree.
The leader of the SNC has dismissed the government's decision as "just a ploy".
Activists say that if the government does withdraw the army, many areas will immediately fall out of its control.