Injured rebels are being transported into Lebanon from the beleaguered city of Qusayr.
A Syrian opposition group has urged all foreign fighters involved in the country’s conflict to leave, regardless of whether they are pro- or anti-government.
The move came as rebels claimed Lebanese Hezbollah fighters have arrived in Aleppo to fight alongside forces loyal to Syrian President Bashar al-Assad.
Hezbollah were also instrumental in the recent take-over of the city of Qusayr by government forces.
There were also reports that Kurdish fighters have joined the Free Syrian Army in some areas of the northern city.
“The coordination body calls on all non-Syrian parties that are taking part in the fighting on Syrian territory, no matter what party they are fighting beside, to leave the country immediately,” said Hassan Abdul Azim, head of the National Coordination Body for Democratic Change, at a news conference in Damascus.
Abdul Azim added that the coalition would seek United Nations condemnation of foreign fighters’ involvement.
“The body considers every non-Syrian who kills in Syria as an aggressor,” he said.
The National Coordination Body for Democratic Change is a coalition of non-armed opposition groups and figures based in Syria.
The Gulf Cooperation Council has also condemned the interference of Hezbollah in the Syrian conflict in a statement on Monday.
Fierce fighting is continuing in Aleppo as Syrian rebels make fresh advances in their battle to seize the Minnigh airbase.
“Opposition fighters have seized the radar tower in the Minnigh airbase,” Syrian Observatory for Human Rights director Rami Abdel Rahman said.
“Fierce clashes have raged in the airbase since dawn Sunday,” he added.
State news agency SANA said the rebel assault had been repulsed.
“Troops from our heroic army stopped terrorist groups from assaulting the Minnigh army airbase,” it said.
Government troops “stopped terrorists from assaulting the airbase through its eastern and western sides” and captured a rocket launcher and heavy machineguns, the report added.
Rebel fighters have been trying to capture Minnigh for months, as part of a strategy to deny the regime the use of air power across Aleppo province.
The UN estimates at least 94,000 people have died in the Syrian conflict since March, 2011.
The issue of foreign fighters in Syria has been thrown into sharp relief recently with the execution of a Syrian teenager by three foreign rebels who accused him of blasphemy.
Mohammad Kattaa was using a phrase common with Syrians when men speaking classical Arabic picked him up and shot him dead.