Bianca Jagger is a prominent human rights campaigner

An Austrian who found a ring belonging to human rights activist Bianca Jagger is suing her for defamation resulting from a row over whether she should pay a reward.

Reinhard Ringler found the ring, worth 200,000 euros ($254,000; £175,000), in Salzburg last year.

According to Austrian law, he is due 5% of the value - 10,000 euros.

Ms Jagger, who was once married to the Rolling Stones singer Mick Jagger, refuses to pay because, according to comments made by her lawyer, Mr Ringler took too long to return the item.

It is claimed that he is not entitled to the reward as he took eight days to give it to the police.

Mr Ringler says he initially gave the platinum and aquamarine ring to his daughter, thinking it was worthless, and only realised its value when he saw reports of the lost ring in the media.

Ms Jagger's lawyer says that, as an alternative, she offered to pay 9,000 euros to Amnesty International and the remaining 1,000 to Mr Ringler's daughter.

The defamation case will be heard at a court in Salzburg in May.

Correction 15 May 2009: The original version of this story, based on an agency report, wrongly stated that Mr Ringler was suing Ms Jagger in connection with a reward for the finding of the ring. In fact, it was an action for defamation based on comments made by Ms Jagger's lawyers. Ms Jagger rejects the allegations.