Three people have been arrested in Norway on suspicion of preparing terrorist attacks.
Unnamed Norwegian and US officials told the Associated Press that the men were members of al-Qaeda and had been under surveillance for a year.
They said it was not clear whether the men had selected a target, but they were attempting to make peroxide bombs.
The BBC's security correspondent says Norway may have been targeted because it has troops in Afghanistan.
"The Norwegian Police Security Service (PST) has today, July 8, 2010, arrested three people suspected of preparing acts of terror," the PST said in a statement on its website.
Prosecutors say the Norwegian case is linked to foiled bomb plots in New York and the English city of Manchester.
Twin plots
On Wednesday, US prosecutors charged five men in New York over a plot to bomb the underground system. The plot was foiled in September.
The New York plot also involved peroxide bombs, prosecutors said. One man, Najibullah Zazi, has already pleaded guilty.
"The charges reveal that the plot... was directed by senior al-Qaeda leadership in Pakistan," the US Department of Justice said in a statement.
One of those charged in New York is Abid Naseer, 24, born in Pakistan and arrested in the north-east of England on Wednesday. The US is now seeking his extradition.
Mr Naseer was remanded in custody by a court in the UK on Wednesday night.
The former construction site worker is suspected of being the ringleader of a plot, thwarted in April 2009, to bomb targets in Manchester city centre
A bid to put him on trial in Britain was aborted last year and his deportation was blocked when a judge said Mr Naseer could face torture in Pakistan.
