At least 50 Syrian army soldiers have been killed by a suicide car bomb in the central province of Hama and at least 20 rebel fighters were killed in an air strike in the northwest province of Idlib, activists have said.
The Britain-based Syrian Observatory for Human Rights said the bombing in the village of Ziyara in Hama province was carried out by Jabhat al-Nusra, an armed group that has claimed several attacks on regime targets.
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The bombing killed more than 50 people, according to the Observatory, a claim which cannot be independently verified.
In Damascus, a car bomb exploded in the western district of Mezzeh killing 11 and wounding dozens more, state-run news agency SANA reported.
Residents said senior security and military officers of Assad's regime live in the area targeted late on Monday.
The Observatory also said at least 20 rebel fighters were killed when Syrian air force jets bombarded the town of Haram in the northern province of Idlib.
The latest developments came as the rebels sought to keep momentum after seizing a major oilfield and shooting down a fighter jet in the eastern province of Deir al-Zor the day before.
Fighting also erupted in southern districts of the capital on the edge of the Yarmuk Palestinian refugee camp in Damascus, the Observatory said, with Palestinian sources saying 31 people had died from shelling at the camp on Sunday and Monday.
Nationwide, at least 192 people were killed in Monday's violence, the Observatory said, including 53 civilians, 85 soldiers and 54 rebels.
In Aleppo, fighting broke out at a roundabout at the northwest entrance to the city in the Zahraa district and on the airport road to the southeast, the Observatory and residents said.
One resident of a district near Zahraa said Monday's fighting in the area was the heaviest in recent days.
"It's been almost one week that we are living in terror at night. We hear everything - gun battles, tank shelling, explosions ... The clashes before dawn today were the worst all week," Samir, a 37-year-old pharmacist, told the AFP news agency.
Members of the Syrian Arab Red Crescent, meanwhile, said on Monday that its main warehouse in Aleppo had burned down amid recent fighting, with the loss of crucial supplies including medicine, food and winter relief items like blankets.
The rebels have scored significant gains in recent weeks and now hold swathes of territory in the country's north, but have struggled to gain ground in and around Damascus and in the commercial hub Aleppo amid heavy bombardment from government air strikes.
The escalating conflict has added urgency to a meeting of the opposition Syrian National Council SNC in Qatar, where the United States is reportedly pressing for a new umbrella organisation to unite the country's fractured opposition.
Syria's main opposition bloc agreed on Monday to broaden its structure to accommodate 13 other groups, a spokesman said.
The decision by the SNC came on the second day of a four-day meeting of opposition groups in the Qatari capital, Doha, aimed at forging a more united front against Assad's regime.
Participants "have agreed a restructuring plan and to reduce the number of [current] members of the general secretariat to accommodate 200 new members representing 13 political groups and independents," said SNC spokesman Ahmad
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Kamel said the existing membership would be reduced from 313 to 220 to pave the way for the additional 200 members. The general secretariat will convene in its revamped form on Tuesday, he added.
The meeting is also expected to discuss an initiative by leading dissident Riad Seif, which appeared to enjoy US support but has encountered reservations from some SNC members, to unite all Syrian groups opposed to Assad.
"We will form a political leadership that will in turn form a government of technocrats," Seif said on Sunday, insisting his proposal was "not to replace the SNC which should be an important component."
The initiative will top the agenda of a broader meeting on Thursday called by host Qatar and the Arab League.
According to the reports, which emerged after US Secretary of State Hillary Clinton said the SNC was not a representative body, long-time dissident Seif is touted as the potential head of a new government-in-exile dubbed the Syrian National Initiative.
Syria's Deputy Foreign Minister Faisal al-Miqdad dismissed the conference, accusing the opposition of following a foreign agenda.
"When the opposition parties follow the desires of Israel, the United States and the Western countries, who stand against the interest of the Syrian people, this then achieves the main goals of such conferences which do nothing but help escalate the situation in Syria," he said.