The governor of Homs said hundreds of Syrian rebels would be evacuated from the last rebel-held area of the city on Monday, prompting rebels to warn that would amount to Damascus declaring the end of a truce.
The tension over the district of al-Waer, the opposition's last foothold in Homs city, piled more pressure on the widely violated ceasefire brokered by the United States and Russia that has been in effect since last Monday.
The government has been seeking to conclude local agreements with rebels in besieged areas to give them safe passage to the insurgent stronghold of Idlib in northwestern Syria.
The opposition to President Bashar al-Assad says such local agreements are part of a policy of forced displacement imposed on besieged populations after years of blockade and bombardment.
Talal Barazi, the governor of Homs, told Reuters that between 250 to 300 fighters were due to leave Waer on Monday.
He said an agreement now in its third phase would be complete within weeks. "At the end of it, Waer will be empty of weapons and gunmen," he said.
A rebel statement signed by prominent groups fighting under the Free Syrian Army banner and the powerful Islamist faction Ahrar al-Sham said the opposition would fight on if an evacuation went ahead.
"If any person is evacuated from al-Waer (district) or any other besieged district in Syria ... the regime will have clearly ended its commitment to any proposed truce, and all the revolutionary factions will continue in their legitimate right to fight it," the statement said.
Waer is home to some 60,000 people.
Some 300 insurgents left Waer for Idlib as part of an agreement concluded last December.
The opposition was dealt a major blow last month when a local agreement resulted in the effective surrender of the insurgent-held Damascus suburb of Daraya to the government.
The rebel statement said the opposition would review the entire political process if "international impotence" continued towards areas besieged by the government.
The Syrian Observatory for Human Rights said a number of fighters and people needing medical attention were expected to be evacuated from Waer on Monday.