UN Secretary-General Ban Ki-moon said it would be "reprehensible" for Syria to use chemical weapons after Damascus warned it could deploy them if it felt threatened by foreign intervention.
Syrian forces have bombarded parts of Damascus with helicopter gun ships, witnesses say, driving rebels out of a northern district a week after opposition fighters launched a major assault on the capital.
Syrian troops and armoured vehicles have pushed into a rebel-held district of Aleppo and struck back in Damascus against fighters emboldened by a bomb attack against President Bashar al-Assad's inner circle.
Rebel fighter Ismail watches approvingly as local villagers loot beer and whisky from the burnt-out duty free shop at Bab al-Hawa, the border post between Syria and Turkey seized from President Bashar al-Assad's forces.
Kofi Annan has arrived in Damascus for talks with President Bashar al-Assad, his spokesman said, a day after the international peace envoy admitted that his peace plan had so far failed to end 16 months of bloodshed.
Clashes in Damascus between state forces and rebels, described by residents as the heaviest fighting to reach the capital since the start of the 15-month uprising against President Bashar al-Assad, spread to a second district, activists said.
Syrian government forces have killled more than 200 people, most of them civilians, in a village in the province of Hama, opposition activists said.
Negotiations on a resolution to extend a UN monitoring mission in Syria have begun between a deeply divided UN Security Council with Russia saying it would not agree to a threat of sanctions in a bid to end the 16-month conflict.
International envoy Kofi Annan has asked the UN Security Council to make clear to Syria's government and opposition that there would be "clear consequences" for not complying with his plan to end the 16-month conflict that has killed thousands.
Syria's conflict spilled further into Lebanon on Saturday when mortar fire from President Bashar al-Assad's forces hit villages in the north, killing five people after rebels crossed the border to seek refuge, residents said.
Kofi Annan does the best he can. At least he's back in harness, doing what he does best: trying to make peace where there is no hope of peace.
Turkey's armed forces command says it has scrambled a total of six F-16 fighter jets in three separate incidents responding to Syrian military helicopters approaching the border on Saturday, but there was no violation of Turkish airspace.
The White House has condemned all acts of violence in Syria, including attacks by insurgents on supporters of the government of President Bashar al-Assad, such as an assault on a pro-government television station in Damascus.
Officials in Turkey say Syrian forces have fired towards a Turkish military transport plane involved in a search for an F-4 reconnaissance jet shot down by Syria last week, but the second aircraft was not brought down.
The Turkish and Syrian navies are conducting a joint search for Turkish airmen shot down by Syria over the Mediterranean, only a short distance from a Turkish province hosting thousands of rebels fighting President Bashar al-Assad.
Syria has shot down a Turkish warplane over the Mediterranean and Ankara has warned it will respond decisively to the incident that threatened a new international dimension to the 16-month revolt against Syrian President Bashar al-Assad.
Syrian President Bashar al-Assad's army has intensified shelling of Sunni Muslim districts in the northwest city of Homs, killing at least 11 people and wounding dozens hours after UN monitors suspended their work, opposition activists said.
The world could slip back into a Cold War over Syria and the sprawling Arab country could break up into two or three warring parts, with unforeseeable consequences for the Middle East, a senior Israeli military commander said.
The smell of burnt flesh hung in the air and body parts lay scattered around the deserted Syrian hamlet of Mazraat al-Qubeir, UN monitors said after visiting the site where 78 people were reported massacred two days ago.
UN monitors seeking to reach the site of a new reported massacre of Syrian villagers by forces loyal to President Bashar al-Assad were shot at with small arms, UN Secretary-General Ban Ki-moon says.