Police have arrested a man who took several hostages at Hillary Clinton's campaign office in Rochester, New Hampshire, ending a lengthy siege.
The suspect is believed to have a history of mental illness
The man, who claimed he had a bomb strapped to his chest, had entered the building and demanded to speak to Mrs Clinton, who was not present.
Armed police rushed to the scene, persuading him to release his hostages and surrender without any conflict.
Mrs Clinton expressed relief that her staff and volunteers were safe.
"It's been a difficult, but eventually gratifying day the way it worked out," said Mrs Clinton, speaking after the suspect's arrest.
"We've had nothing on our minds except the safety of these young people who work for me."
Mrs Clinton was at a Virginia party event and had no part in the stand-off, but headed to New Hampshire to thank police and speak to her staff after it was resolved.
Speaking in Rochester, she said the incident would not deter her or affect her presidential campaign in any way.
Media reports said she cancelled a speech she was just about to make as news of the hostage crisis broke.
The man, who is believed to have a history of mental illness, entered the office about 1300 local time (1800 GMT) and demanded to speak to the US presidential hopeful.
He first released a mother and her baby and later freed two volunteers.
Meanwhile, police had sent a tactical bomb unit and hostage negotiators to the scene.
Hostage negotiators were quickly sent to the scene
Shortly before the suspect surrendered at about 1800 (2100 GMT), the last hostage walked free from the office.
The man has been named by US television networks as Lee Eisenberg. Law enforcement sources told the BBC that the suspect was well-known locally, and had a history of emotional issues.
Reports said he was depressed and may have been drinking heavily prior to the siege.
He had told his stepson to watch the news, according to sources.
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 were also evacuated during the siege.
Mr Obama's office is on the same street as the Clinton campaign headquarters.
Correspondents say that primary campaign offices in US provincial towns are often staffed by small numbers of volunteers and are easily accessible to the public.
New Hampshire is to hold one of the first multi-party primaries of the 2008 presidential election campaign in January, and all of the candidates are currently concentrating much of their campaigning efforts in the state.