Human rights groups working in Syria say at least 28,000 people have disappeared after being abducted by soldiers or militia.

They say they have the names of 18,000 people missing since anti-government protests began 18 months ago and know of another 10,000 cases.

Online activist group Avaaz says "nobody is safe" from a deliberate government campaign of terror.

It intends to give the UN Human Rights Council a dossier for investigation.

Avaaz has gathered testimony from Syrians who says husbands, sons and daughters have been forcibly abducted by pro-government forces.

Alice Jay, campaign director at Avaaz, said: "Syrians are being plucked off the street by security forces and paramilitaries and being 'disappeared' into torture cells.

"Whether it is women buying groceries or farmers going for fuel, nobody is safe."

She said it was a deliberate strategy to "terrorise families and communities".

"The panic of not knowing whether your husband or child is alive breeds such fear that it silences dissent," she said.