Syria's opposition vowed on Wednesday to fight on to topple President Bashar al-Assad, saying any political solution to the conflict must lead to the fall of the regime.
Meanwhile, troops and rebels were locked in fierce clashes on Wednesday night outside the Damascus district of Qabun as the army tried to storm the area, the Syrian Observatory for Human Rights said.
A statement from the opposition National Coalition's came after G8 leaders said they were “committed to achieving a political solution” to the war.
It also called on the United Nations to investigate the alleged use of chemical weapons by Assad's forces in rebel-held areas.
“The Syrian National Coalition is committed to any political solution that puts an end to the bloodshed, and achieves the Syrian people's aspirations to bring down the Assad regime,” it said in a statement.
The group added that it “reserves the right to use all means at its disposal” to bring Assad down, “chiefly military action”.
“The Assad regime has continuously killed civilians using ballistic missiles, chemical weapons and warplanes. It is the only source of terrorism in Syria.
“In order to achieve a lasting peace in Syria, efforts by all countries should be focused on fighting the regime alone.”
Outside the Damascus district of Qabun, the Observatory said at least two rebel fighters have been killed, with others wounded.
“The district has come under continuous, heavy shelling over the last few hours, killing at least two civilians and wounding others,” the Britain-based Observatory said.
The northeastern neighborhood of the capital has been a battleground for months, with the military regularly targeting it with shells and air raids.
Meanwhile, near the capital, fighters from Lebanon's Shiite group Hezbollah joined troops in a push to cut off rebel supply lines.
And the Coalition said it feared a “massacre” was imminent in southern Damascus, as Assad loyalists amassed around rebel areas there.
“Army troops and Hezbollah members fought rebels near the Khomeini hospital in Zayabiyeh village,” southeast of Damascus, said the Observatory.
“Hezbollah fighters, who have a strong presence at Sayyida Zeinab (in southeastern Damascus), are trying to seize control of villages near Zayabiyeh and Babila.”
The army shelled both Zayabiyeh and Babila, the group said.
Hezbollah's Al-Manar television reported that the army was advancing towards Zayabiyeh, just south of the confession ally mixed district of Sayyida Zeinab, named after an important Shiite Muslim shrine.
The Lebanese Shiite movement has been fighting alongside the army for months in the district, which lies in an area that rebels from southern Damascus have used as their main rear base.
Activists say the regime is trying to crush the rebellion on the outskirts of Damascus in order to cut off supply lines to rebel pockets inside the capital.
“There is a fierce campaign against the (rebels) south of the capital... The humanitarian situation is very critical,” said Damascus-based activist Matar Ismail.
Ismail said Hezbollah and the Abu al-Fadl Abbas Brigade -- a mostly Syrian Shiite force that has attracted Shiite fighters from elsewhere in the region -- were playing a key role in the fight.
Hezbollah was also credited with an important role in the army's recapture of the rebel stronghold of Qusayr in central Homs province earlier this month.
The Coalition warned that Assad loyalists are “staging military operations on 10 axes” in Damascus province, as they try to advance on the south of the capital.
It said rebel-held areas are “under blockade. Food and medicines are not being allowed in.”
“Now, regime troops and militiamen backed by Hezbollah and the Abu al-Fadl Abbas Brigade are deploying en masse, with dozens of military vehicles and tanks, rocket launchers and heavy machineguns,” the group said.
Some 120,000 people living in strife-torn southern Damascus “are trapped in... fear that (regime) forces may commit a new massacre” there, saying there may be “no way out” for residents.
Elsewhere, fierce battles broke out between rebels and troops in Idlib, in northwestern Syria, the Observatory said.
Opposition forces captured an army post on the road linking the coastal province of Latakia to Ariha in Idlib province, and two tanks were destroyed.
In other developments, a controversial Salafist sheikh threatened to find a “military” solution to alleged Hezbollah safe houses in a southern Lebanese town, a day after clashes involving his supporters left one person dead.
And Jordanian border guards killed a Syrian and wounded two others after they attacked Jordanian soldiers at the border while trying to enter the country, the army said.
Syria opposition vows to fight on to topple Assad