Elite Japanese troops rappelled from helicopters and soldiers raced across the water in speed boats in a multinational exercise off Japan's coast Tuesday aimed at intercepting weapons of mass destruction at sea.

Nine ships from Japan, the United States, Australia and France joined in the exercises off Tokyo under President Bush's Proliferation Security Initiative (search), or PSI.

The maneuvers, the first in East Asia and the first hosted by Japan, have been criticized by nearby North Korea (search) as a "provocation."

While officials said the exercises are not directed at any one nation, U.S. Undersecretary of State John Bolton (search) said the measures were needed to foil nations like North Korea, which he termed a "serious proliferation problem."

"It's the world's foremost proliferator of ballistic missile technology." Bolton said of North Korea. "But it's important that the PSI be operational worldwide and that it be seen as operational worldwide."

The "Team Samurai" drills, held in the Pacific just south of Tokyo, involved a scenario focusing on the interception and boarding of two ships suspected of transporting sarin, a deadly nerve gas.

As Japanese Coast ships crossed its bow, a squad of specially trained troops rappelled down from helicopters to board the first target ship, which flew a skull-and-cross-bones flag.

Boarding teams from the U.S. Coast Guard, along with Australian and French units, took control of the second ship, racing to it in speed boats and climbing onto it from rope ladders.

Attesting to Washington's interest in pushing the initiative, Bolton and Rear Adm. James Kelly, commander of U.S. aircraft carrier Kitty Hawk, were aboard the Izu, the second of the two targets.

"We regard this activity as extremely important," Bolton said. "We have enormous capabilities on a worldwide basis which are aimed at stopping the illicit trafficking in weapons of mass destruction."

The exercises are part of a U.S. administration effort to block shipments of nuclear, chemical and biological weapons, the material and equipment needed to make them and missiles that could be used to carry them. Seventeen nations, from Turkey to Norway, sent observers to the drill.

"It's a very good opportunity for the nations in the regions to cooperate," said Australian military attache Col. Mark Hoare. "It's a message of resolve."

Eleven similar drills have been held since last September, when Australia hosted the first exercises in the Coral Sea after the initiative was formally backed by 11 nations.

Drills have also been held in the Arabian Sea, when heavily armed U.S. and Spanish troops used military helicopters to track, board and search a vessel disguised as a merchant ship carrying concealed chemical and biological weapons.

The 11 nations that initially backed the PSI initiative last year are Australia, France, Germany, Italy, Japan, the Netherlands, Poland, Portugal, Spain, the United Kingdom, and the United States.

Since then, five other countries have actively participated in the program, while 60 others have declared their willingness to support its goals.

Asked about Asian participation, Bolton said Russia and Singapore had joined the initiative and that China, while not participating, supported the exercises.

"There's certainly more work to be done, to be shared, but I think we're making good progress," Bolton said.