As many as 30 Greenpeace activists broke into a Swedish nuclear plant Monday, demanding that parliament this week vote against allowing new nuclear facilities to be built, the group and police said.

"There are now Greenpeace activists on the premises" of the Forsmark nuclear power plant near Uppsala, north of Stockholm, police spokesman Christer Nordstroem told AFP.

He said it remained unclear how many Greenpeace activists had managed to get into the plant, but the environmental group itself sent out a statement earlier saying around 30 would enter the facility to conduct a peaceful protest against nuclear power use.

"The activists demand that Swedish members of parliament vote 'no' to new nuclear power at a vote on June 17 and instead bet on renewable energy," the group said, adding that the protesters were prepared to stay put until the day of the vote.

Sweden , which has 10 reactors at three power stations, announced last year it had reversed a decision to phase out nuclear power, and the parliament is set to vote Thursday on whether to expand the Scandinavian country's nuclear facilities.

Greenpeace spokesman Ludvig Tillman told the TT news agency several activists had been stopped by guards, but that "many succeeded in getting in".

The activists, who reportedly climbed over a fence to get in, were protesting an expected "decision that will have consequences for hundreds of years if you think of the waste nuclear power creates," he said.

"Replacing existing nuclear plants with new nuclear power would be a mistake of historical proportions," he said in the Greenpeace statement.

Police spokesman Nordstroem said many police were on site.

"We are monitoring the situation," he said.

Forsmark spokesman Claes-Inge Andersson told TT plant authorities were also following closely the protest, but said there was little worry the activists would pose a security risk.

"It is one thing to manage to climb over a fence, but it should not be possible for them to reach the vital parts" of the nuclear plant, he said, adding that the activists "are not here to damage the plant.
They just want to protest a parliamentary decision."