The United States and Panama Wednesday signed an agreement allowing U.S. forces to board and search Panamanian-registered vessels on the high seas suspected of transporting weapons of mass destruction. The accord is part of the U.S.-led Proliferation Security initiative (PSI).

Panama has the largest shipping registry in the world, with nearly 6000 large commercial vessels sailing under its flag. Thus the agreement represents a major expansion of the U.S.-sponsored effort to stop illicit trafficking in nuclear, chemical and biological weapons and related equipment.

Under terms of the accord, an amendment to an existing U.S.-Panamanian agreement against drug trafficking, U.S. naval vessels will be allowed to board, search and possibly detain ships registered in Panama suspected of carrying weapons of mass destruction or other terrorist related cargo.

The agreement is technically reciprocal, giving Panama the right to board U.S. registered ships with suspect cargoes, though Panama's navy, in practice, has little capability beyond the Central American country's own waters.

The United States signed a similar agreement in February with Liberia, which has the world's second-largest ship-registry, with some 2,000 large cargo ships flying its flag.

At the signing ceremony, John Bolton, under secretary of state for arms control and international security affairs, said that, with the addition of Panama, nearly half of the world's shipping, by volume, now comes under the enhanced scrutiny of the Proliferation Security Initiative.

?The combination of Panama, Liberia and PSI core partner countries means that now almost 50 percent of the total commercial shipping of the world, measured in deadweight tonnage, is subject to the rapid-action consent procedures for boarding, search and seizure. It's a very significant threshold to approach. Concluding the PSI ship-boarding agreement further bolsters the reputation of the Panamanian ship registry, and the confidence of those involved in the shipping trade that Panama is taking all steps necessary to ensure that its ships are not misused.?

Panamanian Justice and Interior Secretary Arnulfo Escalono, who signed for his government, said he hoped the accord will serve as a starting point for other hemisphere countries to support the PSI.

He said only by working together can concerned countries, in his words, "cut out the cancer" of the proliferation of weapons of mass destruction.

The United States and 10 key allies were the initial partners in the PSI, which was formally launched by President Bush in an address in Krakow, Poland, nearly a year ago.

The core members of the initiative, joined in March by Canada, Norway and Singapore, have held several sets of joint exercises involving the boarding of ships and planes, and they have stepped-up anti-proliferation cooperation by their intelligence services.

There have been a number of actual interdictions under the PSI. The most notable instance came last October, with the seizure of a German-owned ship found to have been carrying uranium-enrichment centrifuge parts to Libya.

Libya subsequently renounced its covert nuclear weapons program.