BEIRUT (Reuters) - The only way into rebel-held parts of Aleppo was cut on Thursday by a Syrian government advance that put the road within firing range, two rebel sources and a group monitoring the conflict said.

"Currently nobody can get in or out of Aleppo," Zakaria Malahifji of Aleppo-based rebel group Fastaqim, told Reuters.

A second rebel official with fighters in the area said: "All the factions sent reinforcements and are trying to take back the positions taken by the regime, but the situation is very bad, there was heavy regime air cover in the night."

The pro-government forces had advanced in the al-Malah Farms area northwest of Aleppo, bringing them to within 1 km of the Castello road, the Syrian Observatory for Human Rights said.

(Reporting by Lisa Barrington and Tom Perry; Editing by Tom Perry)