Damascus: Security forces killed three people in northwest Syria on Saturday as a punitive EU oil embargo came into effect, a day after anti-regime protests which activists said cost 21 lives.

The latest crackdown by Syrian forces comes despite the European Union slapping Damascus with the embargo, in a move criticised by Syria's longtime ally Russia.

"Two men were killed and five wounded in Maarrat in Idlib region during an incursion by tanks and 50 buses carrying members of the security forces," said the Local Coordination Committees (LCC), which have activists on the ground.

LCC said "another political activist from the central city of Hama was killed in the same way as the other two when the army opened fire on civilians who were watching the troops."

The Britain-based Syrian Observatory of Human Rights said the latest security operation was "to hunt down wanted people," adding that according to an activist in the region, it was "intended to track down the attorney general Hama, Adnan al-Bakkur who recently announced his resignation."

Bakkur had announced his resignation in an Internet video broadcast on Wednesday to denounce the repression. Syrian authorities claim that an "armed gang" kidnapped Bakkur and was extracting "pure lies" under pressure.

The Observatory further said that authorities had on Saturday "put a body, which had visible signs of torture, of a resident from the town of Qusayr in front of his family home after detaining him for more than a month."

"The relatives of the young man refused the day before Friday to take delivery of the body because the authorities asked them to sign a report accusing terrorist gangs of killing" him, the Observatory said.

On Friday, widespread demonstrations were repressed by security forces, who killed at least 21 people, it said.