- NEW: Video footage posted online shows the man running toward the court in flames
- NEW: The man, whose identity is unknown, is being treated in a hospital, Oslo police say
- Police say they do not know what motivated him to act in this way
- Anders Behring Breivik is on trial on charges of committing acts of terror and voluntary homicide
(CNN) -- A man set himself on fire Tuesday outside the court in Norway's capital, Oslo, where Anders Behring Breivik is on trial over terrorist attacks last summer that killed 77 people.
"We don't know much about his motives, but he set himself alight outside the courthouse. Police were quick to put the fire out, and he has now been taken to hospital," Unni Groendal, head of media for Oslo police, told CNN.
The man, whose identity is not known, was given first aid treatment on site, according to police.
He did not try to force his way through the cordon outside the district courthouse as some reports have suggested, police said.
Breivik claims killing was 'necessary' 
Alleged mass killer shows no remorse 
Prosecution concerned with Breivik sanity Norwegian daily newspaper VG reported that several court employees ran out with water bottles to pour water over the man.
Video posted on the VG website shows the man running toward the court building with his hat and jacket on fire. Police officers then pull off his clothing and try to extinguish the flames as he lies on the ground.
The area has been cordoned off, police told CNN.
The incident happened about 1:45 p.m. local time (7:45 a.m. ET), according to Norwegian TV channel TV2.
Breivik is on trial on charges of voluntary homicide and committing acts of terror in the July 22 attacks. He admits carrying out an attack on a youth camp on Utoya Island and a bombing in Oslo that killed eight people.
He boasts of being an ultranationalist who killed his victims to fight multiculturalism in Norway.
Experts' assessment of Breivik's sanity will be a factor in determining what punishment he receives if convicted. Sentencing options could include imprisonment or confining him to a mental facility.
Friday's court session was disrupted when the brother of one of those killed threw a shoe toward Breivik, hitting one of his defense lawyers.
This week, the court is hearing testimony from some of those injured during Breivik's gun rampage on Utoya Island.
CNN's Per Nyberg contributed to this report.
