More than 900 civilians have been killed in Eastern Ghouta since Syrian regime forces launched a blistering assault on the rebel enclave on February 18, the Syrian Observatory for Human Rights said, as an aid convoy planned for Thursday to bring assistance to besieged civilians did not go through. The death toll reached 905 after fresh air strikes on the town of Zamalka killed seven civilians, the Britain-based monitor said. The Syrian forces are poised to slice the area in two as forces advancing from the east link up with troops at the enclaves western edge, Reuters quoted a pro-Damascus commander as saying on Thursday. The advance by the regime, backed by Russia and Iran, puts the zone effectively under the control of Bashar Assad as the remaining strip of territory was within weapons range. But Wael Alwan, the spokesman for Failaq al-Rahman, one of the main rebel groups in eastern Ghouta, denied that the territory had been cut in half. "No" he said in a text message when asked if the report was correct. Meanwhile, according to the Observatory, dozens of people were treated for breathing difficulties after air strikes slammed into Eastern Ghouta late Wednesday, with medics reporting symptoms consistent with a toxic attack. It said at least 60 people were left struggling to breathe after air strikes and barrel bombs hit the towns of Saqba and Hammuriyeh. Doctors at one medical facility in Eastern Ghouta said they treated at least 29 patients with signs of exposure to chlorine. United Nations investigators say regime forces used chlorine as a weapon at least three times between 2014 and 2015, as well as sarin gas in 2016.  Also Thursday, a convoy of humanitarian assistance expected to enter the enclave was postponed, the International Committee of the Red Cross told AFP.  The joint convoy between the ICRC, United Nations, and Syrian Arab Red Crescent was expected to deliver aid to Eastern Ghoutas main town of Douma. It marks the second time this week that aid operations to the enclave have been disrupted by military developments, with food deliveries cut short on Monday due to heavy bombardment.