Al-Mauritani, described by some to be the organization's "foreign minister," central to the group's plots against the West, was detained in the western city of Quetta, along with two other al-Qaida operatives. In Washington, a U.S. official called al-Mauritani's capture "another major blow to al-Qaida."

Al-Qaida was already reeling from the death in May of its founder, Osama bin Laden, and the elimination, by a U.S. missile strike last month in Pakistan's tribal area, of its new deputy leader, Atiyah Abd al-Rahman, according to U.S. officials.

Since the discovery of bin Laden in the northern Pakistani town of Abbottabad by U.S. special forces, there has been intense pressure on the Pakistani authorities to prove that they're committed to the fight against al-Qaida.

The U.S.-Pakistani collaboration over the capture of al-Mauritani was in contrast to the bitter recriminations from both sides that followed the unilateral bin Laden raid, which threatened to sink the alliance and had, in effect, frozen intelligence cooperation. White House spokesman Josh Earnest hailed the arrest as "an example of the longstanding partnership between the U.S. and Pakistan in fighting terrorism."

Al-Mauritani "was tasked personally by Osama bin Laden to focus on hitting targets of economical importance in United States of America, Europe and Australia," said a statement from the Pakistani military. "He was planning to target United States economic interests, including gas and oil pipelines, power-generating dams, and strike ships and oil tankers through explosive-laden speed boats in international waters."

Bin Laden had long been obsessed with trying to cripple the U.S. and its allies economically, realizing that militarily it would be impossible.

Al-Mauritani "is a seasoned, senior operative trusted by the group's top leaders. He played an absolutely central role in planning and coordinating al-Qaida's operations in Europe, plots that targeted both European and American interests," said the U.S. official, who requested anonymity to discuss the highly sensitive matter. "The U.S. provided critical lead information and technical assistance in working with Pakistan to eliminate the threat posed by this terrorist."

The U.S. official provided no further details of the U.S. role in the capture, but asserted that the speed-boat plan and other plots were "aspiration," and may not have moved into the actual planning stages.

"The Pakistanis deserve real credit for their hard investigative and operational work in taking deadly threats like al-Mauritani off the battlefield," the U.S. official said. "There is clearly more to be done, and both sides recognize the imperative of acting together against these dangerous targets."

The arrest of al-Mauritani was "planned and conducted with technical assistance" from American spy agencies, the Pakistani military said, adding that intelligence co-operation between the countries is "intimate."

Among the papers recovered from bin Laden's compound in Abbottabad was reportedly a document written by al-Mauritani, where he sets out plans to attack economic targets in Europe. That multi-city plot, which involved Britain, France and Germany, was uncovered after the arrested of two German jihadists last year, triggering a terror alert in Germany. According to reports, the two had been recruited by al-Mauritani in 2009 in Pakistan's tribal area, where he allegedly told them that "what we're planning, not even the devil has in mind."