British police arrest environmental activists targeting Canadian PM Harper's visit

British police have arrested several environmental activists who allegedly breached Parliament security to protest Canadian Prime Minister Stephen Harper's visit.

The activists, who campaign against using oil from Canada's tar sands, say they entered the Parliament building and climbed onto its roof to protest as Harper visited to deliver a speech to lawmakers.

The Metropolitan Police said two men and a woman were arrested Thursday for trespassing on a protected site in Parliament. Two other women were arrested outside on suspicion of criminal damage.

Environmental groups have been pressuring Harper over tar sands oil, which they say is more of a threat than lighter forms of crude because of the dangers of spills and because it produces more of the greenhouses gases blamed for global warming.