Britain has condemned the "horrific" bomb blast in Oslo that has left at least seven people dead.
Foreign Secretary William Hague said the UK stands "shoulder to shoulder" with Norway following the terrorist attack, which severely damaged the prime minister's offices.
The statement of support came as diplomats sought to check whether any British nationals were caught up in the carnage.
Fears that Norway may be the victim of a co-ordinated series of attacks were sparked after a gunman opened fire at the Norway Labour Party's youth camp outside Oslo, shooting several people. One person has been arrested, according to reports.
Mr Hague said: "I send my deepest condolences to all those who have lost relatives or been injured in today's horrific bomb blast in Oslo.
"Our Embassy stands ready to provide assistance to any British nationals who may have been caught up in the attack.
"We condemn all acts of terrorism. The UK stands shoulder to shoulder with Norway and all our international allies in the face of such atrocities.
"We are committed to work tirelessly with them to combat the threat from terrorism in all its forms."