In a rare interview with the UK’s Sunday Telegraph newspaper, Mr Assad said involvement risked transforming Syria into “another Afghanistan”.
His comments came after the UN secretary-general made a new call for the repression to end.
At least 50 civilians and members of the security forces were killed on Saturday, according to the two sides.
Activists said 21 civilians were killed and that army tanks had shelled a historic district in the city of Homs.
The government said 20 soldiers had been killed in Homs, and 10 members of the security forces killed during an ambush of their bus in Idlib province.
More than 3,000 people have died in the unrest since protests calling for the government of Mr Assad to step down broke out in March.