Two people taken hostage at a Hillary Clinton campaign office in New Hampshire have been freed, reports say.
The hostage-taker entered the building in the city of Rochester hours earlier, claiming to have a bomb.
It is not known whether other people are still being held inside the building. TV pictures have been showing police taking up positions nearby.
Mrs Clinton is at a Democratic Party event in Virginia and has not been involved in the siege.
The area has been evacuated and police have sent a tactical bomb unit and hostage negotiators to the scene, according to a New Hampshire police spokesman.
Law enforcement sources have told the BBC that the suspect is well-known locally, and has a history of emotional issues.
He had told his son to watch the news, according to sources.
The man earlier released a mother and her baby but held onto two volunteers, according to police.
Local shopkeeper Lettie Tzizik told local television station WMUR TV: "A young woman... came rushing into the store just in tears, and she said: 'You need to call 911 - a man has just walked into the Clinton office, opened his coat and showed us a bomb strapped to his chest with duct tape'."
The offices of rival presidential candidates Barack Obama and John Edwards have also been evacuated.
Mr Obama's office is on the same street as the Clinton campaign headquarters.
New Hampshire is due to hold the first primary of the 2008 presidential election campaign in January, and all of the candidates are currently concentrating much of their campaigning efforts in the state.