BEIRUT: The opposition Syrian National Coalition said Sunday that regime forces are preparing to launch a major assault on rebel-held areas of the northern city of Aleppo.
The group's leadership, meanwhile, was meeting in Istanbul to elect a successor to SNC chief Ahmad Jarba.
"The military situation is very difficult, the siege of Aleppo has become a reality," coalition spokesman Luay Safi said on the group's website.
"Syrian troops are preparing to invade Aleppo," he said.
Aleppo, once Syria's commercial hub, has been divided since a July 2012 rebel offensive. Government aircraft have been targeting opposition-held areas there as well as nearby towns and villages.
The assault began in mid-December and intensified in January, with helicopters raining down barrels bombs, causing a massive exodus.
Regime troops have made advances since last week, taking control of most of the industrial district in northeastern Aleppo and threatening to cut off rebel supply lines.
On Sunday, pro-government daily Al-Watan said loyalist troops were on the verge of "another breakthrough" by routing rebels from a military academy in the city's northeast.
Rebels fighting to topple Syrian President Bashar al-Assad control eastern parts of Aleppo and some districts in the north.
Loyalist forces are mostly in control of southern districts of Aleppo as well as some western areas.
Opposition coalition spokesman Safi charged that government forces around Aleppo were acting in collaboration with the jihadist Islamic State.
He condemned the West's failure to support the rebel Syrian Free Army, which is fighting both Assad's forces and IS.
"To this day the United States is preventing the dispatch of sophisticated weapons to the Free Syrian Army to fight Assad's terrorism and radical organisations," he said.
IS has seized large swathes of territory in Syria and neighbouring Iraq, declaring the land it holds to be an Islamic "caliphate", and its leader the ruler of all Muslims.
With government forces also on the offensive, SNC official Bahiya Mardini told AFP that the opposition at their meeting in Istanbul would elect a new president on Monday.