United States and British intelligence are tracking three mystery cargo ships for fear they contain Saddam Hussein's weapons of mass destruction, according to British reports.

The vessels left port in late November, just as United Nations weapons inspectors arrived in Iraq to search for chemical, biological and nuclear weapons believed to have been stockpiled since the Persian Gulf War.

They've been traveling in "ever-decreasing circles" ever since, all the while maintaining radio silence in violation of international maritime law. The captains refuse to reveal the content of their cargoes or destinations, according to the Independent and the Evening Standard.

The ships, each with a deadweight of 35,000 to 40,000 tons, were chartered by a shipping agent based in Egypt and are flying under the flags of three different countries, according to the British papers.

Officials believe the ships set sail from a country other than Iraq to avoid detection from Western naval vessels patrolling the Gulf. Defense experts speculate that, if the ships are carrying weapons of mass destruction, the arms could have been smuggled out through Syria or Jordan.

The vessels are thought to have spent much of the past three months in the deep waters of the Indian Ocean. They berthed in a handful of Arab countries, including Yemen.

Asked to comment on the Independent report, a spokeswoman for Britain's Ministry of Defense told Reuters News Agency: "We don't discuss intelligence issues."

The British papers report U.S. and British military forces are reluctant to stop and search the vessels for fear that such intervention could lead to the destruction of "smoking gun" evidence that Hussein is in "material breach" of U.N. resolutions seeking his disarmament.

In addition, if weapons of mass destruction were dumped overboard, the environmental damage could be catastrophic.

U.N. weapons inspectors have found no evidence of weapons of mass destruction after conducting more than 400 searches of 300 sites over the past eleven weeks.

But chief inspector Hans Blix reported to Security Council members that Iraq had failed to account for 1,000 tons of chemical agent, 6,500 chemical bombs, 25,000 liters of anthrax, 38,000 liters of botulinum toxin, 500 tons of sarin, mustard gas and VX nerve agent and 380 rocket engines useful in the delivery of biological and chemical agents.

"One must not jump to the conclusion that they exist. However, that possibility is also not excluded," he said.