The Syrian Observatory for Human Rights has said that government forces seized Sakhour district from rebels in the region, The Guardian reported on Monday. While one rebel official denied the development, another said the situation was still unclear. The English daily quoted an unidentified government official, who said the rest of the northern sector will be taken over soon.

The observatory’s director Rami Abdulrahman said, “It is the biggest defeat for the opposition in Aleppo since 2012. The opposition has lost more than a third of the area it controlled in Aleppo city during the big advance.” The recapture is a major win for Syrian president Bashar al-Assad-backed troops with the capture of rebel strongholds Masaken Hanano and Jabal Badra districts over the weekend. The takeover has split the rebel-held enclave in the east of the city.

The observatory said 219 civilians lost their lives in the exchange of fire over the weekend and that the toll may rise. Speculation that Russian President Vladimir Putin-backed forces have plans to take advantage of the transition in the US presidency to seize control over Aleppo has also surfaced, The Guardian reported.

Fighting between forces loyal to Assad and rebel groups intensified after a ceasefire deal broke down in September when an aid convoy was bombed in Aleppo. More than 3,00,000 people have died in the six-year-long civil war and nearly half the country’s population has been forced to flee since it began.