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A naval training exercise led by the United States and aimed at blocking smuggling of nuclear weapons began Sunday in the Persian Gulf, the first of its kind since North Korea's nuclear test and the renewed U.S. drive for sanctions against Iran.

Iran called the two-day maneuvers "adventurist," but the Foreign Ministry said Tehran's response would be "rational and wise."

"We are watching their movements very carefully," Foreign Ministry spokesman Mohammad Ali Hosseini said, adding that the exercises would not improve security in the Gulf, through which about 20 percent of the world's oil transits.

The maneuvers were taking place under the US-led Proliferation Security Initiative, designed to counter trafficking in weapons of mass destruction, their delivery systems and related materials "to and from states and non-state actors of proliferation concern around the world," the U.S. Navy said.

Two previous exercises have taken place in the region under the 75-nation initiative, among two dozen worldwide since such exercises began in 2003.

It is the first such drill since North Korea's Oct. 9 nuclear test. Observers believe the PSI program could be used to halt North Korean weapons traffic in accordance with U.N. sanctions.

South Korea, which has balked at joining the initiative, sent an observer delegation to the Gulf but declined to participate.

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"We have not (fully) participated in the PSI because there is a high possibility of armed clashes if the PSI is carried out in waters around the Korean peninsula," Vice Foreign Minister Yu Myung-hwan told Parliament Friday.

The exercise comes as the United States is seeking support for U.N. sanctions against Iran for its nuclear program. On Friday, Iran stepped up its uranium enrichment program in defiance of international demands.

Late Sunday, Iranian state television quoted the country's navy chief, Admiral Sajjad Kouchaki, as saying the presence of American warships in the Gulf "indicates the hostile nature of the U.S. policy" and that Iran "is completely ready to confront any possible threat."

However, state television played down the exercise, saying the United States "wanted to exaggerate this small but exhibitionist maneuver." It noted that naval maneuvers had been held "many times in the past."

A U.S. Coast Guard cutter is the only American ship among the nine vessels taking part in the exercise, code-named "Leading Edge." The ships are being commanded at sea from an Italian navy frigate, according to Lt. Cmdr. Charlie Brown, spokesman for the Bahrain-based U.S. Fifth Fleet.

The exercise takes place in crowded international waters off Bahrain, a tiny island kingdom and U.S. ally that lies across the Persian Gulf, about 200 kilometers (120 miles) from Iranian territorial waters.

Brown stated the exercise was not openly aimed at any country and would not affect Iranian vessels or ships heading to Iran.

Two U.S.-led multinational task forces already intercept and search suspicious ships in the Gulf and nearby waters but focus on shipments headed to Iraq, not Iran. Most searches are done with permission of vessel captains, the U.S. Navy has said.

But a U.S. State Department official speaking on condition of anonymity, because of the sensitivity of the topic, said PSI members can halt and board Iran-bound ships if they are suspected of carrying banned shipments.

U.S. authorities say legal authority for searching ships and seizing weapons cargo lies with national laws backed by a pair of U.N. Security Council resolutions ordering states to use border controls to prevent WMD shipments.

Washington has sought deeper cooperation from its Gulf Arab allies in halting nuclear-related shipments to Iran, but many governments are loath to be seen publicly backing the Americans.

The training occurred as coalition naval forces in the Gulf were on heightened watch for possible terror threats to oil facilities in Saudi Arabia and Bahrain.

Sunday's training scenario focused on surveillance, with teams in 16 countries tracking a ship suspected of carrying outlawed weapons components, Brown said. A British Royal Navy tanker played the role of the suspected weapons carrier. He declined to describe the surveillance technology being used.

On Monday, naval forces on eight other vessels are expected to stop, board and search the suspect ship, Brown said. No ammunition or blanks are due to be fired during the mock chase.

Countries taking part include Italy, France, Australia, United States and Britain, with one ship each, and Bahrain with three naval vessels. The U.S. Navy is coordinating the exercise from Fifth Fleet headquarters in Bahrain, Brown said.

Bahrain's participation marks the first time an Arab nation joins an exercise under the three-year-old PSI.

Kuwait, Qatar and the United Arab Emirates, three Arab countries on the Gulf, offered a measure of support as observers. Other observers include Russia, and Japan. Saudi Arabia, the largest of the Gulf countries, has not joined them.

Real-life interdictions have happened in the past. In 2003, U.S. warships intercepted a German-owned ship, the BBC China, bound for Libya with Pakistani-designed uranium centrifuge parts.

In 2005, Secretary of State Condoleezza Rice mentioned 11 intercepts under the PSI program. Among them were halted two WMD-related headed for North Korea and ballistic missiles and nuclear-related components steaming for Iran.

But in 2002, an attempted seizure failed. A Spanish warship intercepted a North Korean-crewed freighter carrying Scud missiles to Yemen. The Scuds were allowed to pass because neither North Korea nor Yemen had signed treaties aimed at halting sales or transfers.