A military vehicle fires and smoke pours from a building.

This video purports to show Homs, Syria - once a stronghold for rebel fighters battling Syrian President Bashar al-Assad - under attack by government troops on Tuesday.

Obtained online, the footage cannot be independently verified by Reuters.

Opposition activists say Syria's military killed 31 people in Homs and other opposition areas on Tuesday, as a deadline drew near for Damascus to withdraw troops as promised under an international peace plan drew near. Six government soldiers were also killed in the fighting, according to activists.

Diplomats say Assad has until midnight Syria time to pull his forces. A full truce is set to start by 6 a.m. on Thursday.

Meanwhile, Syria's foreign minister wants a guarantee that insurgents will honor the truce...a last minute demand now fueling doubts that the peace plan can keep a 13-month uprising from sliding into civil war.

Katharine Jackson, Reuters.