The recovered painting - Conversation with the Gardener by Renoir

"We weren't looking for the painting so it was a bonus when we found it," Stockholm police spokesman Kurt Hansson said.

The Swedish National museum has confirmed that the recovered painting is one of the three stolen.

Raid

On 22 December last year, masked raiders snatched a self-portrait by the Dutch master, Rembrandt, and two works by the French impressionist Renoir - together worth an estimated $30m (�20.9m) - before escaping by boat.

The three thieves walked into the museum in central Stockholm as it was preparing to close for the day.

One, armed with a machine gun, held up security staff while the other two ran to different rooms upstairs

After ordering guards there at gunpoint onto the ground, the two thieves went straight for their target paintings.

Rembrandt self portrait from 1630

Within moments all three had left the building and sped off into the darkness on a small motor boat waiting for them near the museum.

Ransom

Other people are also thought to have been involved in the crime, as two phone calls reported car fires in the area at the same time that the gallery alarm went off at police headquarters.

The subsequent confusion apparently gave the robbers the time they needed to escape.

In January, police received photographs of the stolen paintings and a demand for "several million kronor" for their return, but they refused to pay up.

Several men have been either arrested or are wanted for questioning about the theft.

Detail of Jeune Parisienne by Renoir

Still missing are a Self Portrait (1630) by Rembrandt, and Renoir's Jeune Parisienne.

The museum will not place a precise value on the works, saying only that they are worth millions of dollars.

None of the paintings were insured and the police believe they are still in Sweden.

Reward

The museum remains hopeful for their recovery and has offered a reward for information.

"We hope this feat by the police will lead us to the other paintings," said museum director Torsten Gunnarsson.

The theft is the biggest in Sweden since robbers cut through the roof of Stockholm's Modern Museum in 1993 and stole eight works of art by cubist masters Pablo Picasso and Georges Braque worth about $60m (�41.9).

All but one of the paintings were found - Braque's work Still Life is still missing.