The announcement comes after a massive assault launched by Syrian government and allied forces on February 18 to retake the enclave, which had been out of regime control since 2012.
According to the Syrian Observatory for Human Rights, a Britain-based monitor, at least 1,700 civilians have been killed in bombardment on the enclave in eight weeks.
Douma is the main town in what at the start of the year was a sprawling semi-rural area just east of Damascus, home to almost 400,000 inhabitants.
The regime has been accused of carrying out a chemical weapons attack last week on the town of Douma, the final part of the enclave where rebels were balking at a Russian-brokered deal to evacuate them to northern Syria.
A team of experts from the Organisation for the Prohibition of Chemical Weapons is currently in Damascus and expected to investigate the site of the alleged chemical attack.
The aerial blitz the regime and Russia launched in mid-February has caused extensive destruction in the region's towns.
"Engineering units are starting to clear the mines and explosives sewn by the terrorists in the town to allow the rest of the units to secure the liberated areas and prepare them for the return of civilians to their homes," the army spokesman said.
Thousands of civilians who fled the offensive have already returned to areas previously retaken by the army and allied forces.
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