Swedish police say they have arrested four people suspected of assaulting security guards and trespassing at the government headquarters in Stockholm.

Swedish news agency TT says those arrested were environmental activists planning a stunt as part of a campaign urging the government to close state-owned utility Vattenfall's coal operations in Germany.

The activists climbed ladders to get onto the roof of the entrance of the building, where they unfurled a banner.

Police received reports of an altercation with security officers guarding the entrance, but said no one was injured.

The government is expected to decide soon whether to approve a bid from Czech investors for Vattenfall's coal mines and power plants in Germany. Climate activists say the government should dismantle the coal assets, instead of selling them.