Members of the organization UFO-Sweden are currently knocking on doors nationwide in a bid to follow up on reports of strange phenomena sighted in the skies.

According to chairman Clas Svahn, UFO-Sweden receives an average of one report per day of peculiar flashes, aircraft and extra-terrestrial beings.

Ninety percent of all reports concern easily explainable atmospheric light phenomena. At one point, many sightings could be traced to secret missile launches in the then Soviet Union.

"Today we can explain much more than we could thirty years ago. But there are some genuinely strange cases," said Svahn.

He takes as an example a pilot and his student who took off from Kiruna for a night-time lesson. Suddenly they saw a brightly lit object suspended above an abandoned village ten kilometres ahead. As they approached, the object began to move, lighting up a vast swathe of the countryside before flying away into the night.

"Quite a simple observation really, but incredibly mysterious," said Clas Svahn.

One of those interviewed by UFO-Sweden on the organization's nationwide tour is Niklas Johansson, who is still puzzled by a sighting he made all of seventeen years ago.

One summer's morning at 4am, Johansson was driving to hospital with his wife and daughter when he spotted a blinking, graphite grey object in a corn field near Kristianstad in southern Sweden.

"It was hair-raising. I became very excited and very scared," he said.

At the top of the object were two lights, one green and one yellow. Johansson pulled over to the side of the road and spent several minutes just staring in to the field.

"I would really like an explanation for what I saw. It was something that wasn't supposed to be there," he said.

On his way back from the hospital all those years ago, Johansson stopped off at the field. There he claims that the corn was flattened in a circular form and there were no signs of any footprints or wheels.

He regrets now that he didn't leave his car and approach the unidentified object.

"But you just don't know what might have happened. If it actually was some strange aircraft, there is no way of knowing whether they would have been friendly or hostile," he said.