Stockholm police say they have closed off and evacuated parts of the city center because of threatening behavior by a man who claims he has a "dangerous object" on him.

A police statement says officers were negotiating with the man, who was holed up in an office in the popular shopping and tourist venue of the old town in an apparent political protest. It did not identify the man or give more details.

Local media showed ambulances, fire engines and rescue vehicles on standby and reported that a special bomb unit was sent to the scene.

Swedish news agency TT said the alarm was raised soon after 2 p.m. local time (1200GMT) Thursday when the suspect walked into the offices of a human rights organization.