Syrian rebels in the northern city of Aleppo are waging fierce clashes against government forces in an attempt to prevent opposition neighborhoods from falling under siege.
Government forces have gradually been retaking ground in and around Aleppo for months and now appear poised to cut off rebel-held parts of the city if rebels are not successful in stopping their advance.
"No one knows what to expect, anything can happen," said Omar Nasir, a fighter with the Ansar Al-Haq group in Aleppo. "The regime is using all its strength here."
The opposition is said to control more than half of Aleppo but is surrounded by the government to the east, south and west, leaving about 12 miles of border open to the north. The Syrian government has been on a slow trajectory to retake Aleppo since October, when it seized Safira, a strategic town south of Aleppo, and surrounding villages.
The advance has come about as rebels in northern Syria have been distracted by increasing aggression from the al-Qaida splinter group Islamic State of Iraq and Syria. Initially seen as an ally, ISIS has taken over opposition areas, attacked rebels and forced their extremist brand of Islam on residents. In early January, open hostilities broke out between the rebels and ISIS.
Rebels also blamed a dwindling of arms shipments leaving them less equipped than before to face the well-armed government troops and allied fighters from the militant group Hezbollah.
The threat of an Aleppo blockade comes as numerous besieged neighborhoods in the capital, Damascus, and the central city of Homs have struck truces or temporary ceasefires with the government in order to allow aid to enter and some residents to leave.
More than 250,000 people are estimated to be living under siege, according to the most recent report by a U.N. independent commission of inquiry on Syria. The government has used siege warfare as part of its military strategy across the country, the commission reported. The rebels have also used the tactic, though to a lesser extent.
In January, ahead of peace talks in Geneva, the Syrian government proposed a ceasefire in Aleppo and a prisoner exchange with the opposition. The plan was immediately rejected by the opposition, which accused the government of trying to seem the peacekeeper even as it pursued an intense bombing offensive.