Sweden is urging Amnesty International to study its pioneering prostitution law, amid disappointment over the human rights group's vote to back the decriminalisation of the sex trade, Foreign Minister Margot Wallstrom said.

In a highly controversial move, Amnesty delegates on August 11 voted in favour of supporting the decriminalisation of prostitution for buyers and sellers.

Sweden is strongly opposed to the decision.

It was the first country in the world in 1999 to make it illegal to pay for sex in a bid to quash demand.

Wallstrom told AFP in an interview late Wednesday she was "very surprised" by Amnesty's decision.

"They've lost a lot and not gained very much by doing so. There are a lot of people who have left Amnesty," she said.

"We think there is good reason for Amnesty to come here and look at our system," she said.

She said the foreign ministry planned to invite Amnesty International Secretary General Salil Shetty to Stockholm.

"This is important for all of us that are out in the world talking about human rights and these issues," Wallstrom said.

The Swedish model has been followed in Norway, Iceland, Northern Ireland and Barcelona.

However, the effects of the law remain up for debate in Sweden.

Street prostitution has been virtually wiped out, and some researchers have claimed that the law has helped decrease human trafficking. But a study published by public health officials in March showed that prostitution exists as before but has simply moved online and underground.