The alleged Norwegian plot, underscoring changing al-Qaida tactics in the decade since the 9/11 attacks, was said to involve powerful peroxide bombs similar to ones aimed for detonation in New York and Manchester, England.
All three plans were organized by Saleh al-Somali, al-Qaida's former chief of external operations, who had been in charge of plotting attacks worldwide, Norwegian and U.S. officials believe.
Al-Somali was killed in a CIA drone airstrike last year, but officials say the three plots had already been set in motion by the time of his death.
Thursday's arrests suggested how decentralized and nimble al-Qaida has become since the Sept. 11, 2001, attacks in the United States. The terror group has recently focused on smaller-level attacks that don't require the intricate planning that it took to hijack airplanes and fly them into buildings in New York and Washington.
Last year, when the FBI and CIA thwarted the suicide attack in the New York subway, officials called it the most dangerous plot since 9/11. And in the past two days, revelations about the related plots in England and now in Norway have illustrated the terror group's multi-country scope.
Al-Qaida keeps its plots compartmentalized, and officials do not believe the suspects in Norway knew about the other cells involved. The Norwegian and U.S. officials spoke on condition of anonymity because they were not authorized to discuss the case.
The officials said it was unclear whether the men in Norway had perfected the bomb-making recipe, but Janne Kristiansen, head of the country's Police Security Service, said, "According to our evaluation, the public has never been at risk."
Al-Qaida's No. 2 leader, Ayman al-Zawahri, has called in the past for attacks on Norway. Magnus Norell, a terrorism expert at the Swedish Defense Research Agency, said Norway's 500 troops in Afghanistan could have been a factor, as could a 2006 controversy that arose after a Danish newspaper's publication of cartoons depicting the Prophet Muhammad that enraged Muslims.
It was unclear whether the trio had selected a specific target in Norway, but the alleged plot already had played a role in Norway's decision to raise its terror alert level last year.
"The threat of terrorism in Norway was generally low in 2009. However, certain groups are engaged in activities that could quickly change the threat level in 2010," Norway's Police Security Service wrote in February. Prime Minister Jens Stoltenberg acknowledged Thursday that statement was referring, at least in part, to the al-Qaida plot.
The three captured men, whose names were not released, had been under surveillance for more than a year as the FBI and CIA worked with Norwegian authorities.
"The FBI worked closely with our law enforcement partners in England and Norway throughout the investigation," FBI spokesman Richard Kolko said.
Two suspects were arrested in Norway. A third was captured in Germany, where he was vacationing, the Frankfurt general prosecutor's office said. Norway's Police Security Service said the arrests made in Norway took place in the Oslo area. Kristiansen said all three men "had connections to Oslo."
Those arrested in Norway included a 39-year-old Norwegian of Uighur origin who has lived in the country since 1999 and a 31-year-old citizen of Uzbekistan who had a permanent Norwegian residency permit, Kristiansen said. The man arrested in Germany was a 37-year-old Iraqi with a Norwegian residency permit, he said. German authorities were preparing to extradite him to Norway.
The Uighur traveled to Pakistan's lawless tribal region of Waziristan around the same time as Najibullah Zazi, one of the would-be New York bombers, but the two did not attend the same training camp or meet, a U.S. official said.
The Associated Press learned of the investigation in recent weeks and approached U.S. and Norwegian officials. Authorities told the AP that reporting on the case could jeopardize public safety and allow dangerous suspects to go free. The AP agreed not to report on the investigation until arrests were made.
"AP's knowledge of the case was only one of several factors that was taken into consideration when deciding on the timing of the arrests," Police Security Service spokesman Trond Hugubakken said. "It was not the decisive factor."
U.S. and Norwegian counterterrorism officials worked together to unravel the Norwegian plot, officials said. Kristiansen traveled to the U.S. this spring to discuss closely held intelligence gathered in the case.
The arrests brought strong media attention in Norway, and Stoltenberg urged Norwegians not to racially profile.
"These are separate individuals that are responsible for criminal acts," Stoltenberg said. "It is always bad to judge a whole group of people from what individuals are doing and that is independently of what group these people belong to."
In an indictment unsealed Wednesday in federal court in Brooklyn, prosecutors added several al-Qaida figures to the New York case, including Adnan Shukrijumah, a most-wanted terrorist. The U.S. is offering a $5 million reward for information leading to his capture.
Shukrijumah, one of the al-Qaida leaders in charge of plotting attacks worldwide, was directly involved in recruiting and plotting the New York attack, prosecutors said.