A Syrian loyal to President Bashar al-Assad was stabbed to death by a Syrian dissident in Beirut on Wednesday, Lebanese security sources said.

The killing tinged the Lebanese capital with violence from the conflict in neighbouring Syria for the first time since the uprising against Assad began 16 months ago.

Lebanese security said the pro-Assad man was leaving his work in bustling Hamra street in the early hours on Wednesday when the dissident approached him and stabbed him with a spear.

"It seems they knew each other and the dissident was watching him. He arrived on a motorbike and then when he saw him he stabbed him," a security source said.

Thousands of Syrians fleeing the violence raging in their country have sought refuge in Lebanon.

[Reuters]