Kuwait today arrested three Islamic radicals allegedly planning to attack the growing U.S. military force assembling in this Persian Gulf emirate in preparation for a possible invasion of neighboring Iraq, the Interior Ministry announced.

The three men, all Kuwaitis who expressed sympathy for Osama bin Laden, were plotting to ambush one of the many U.S. military convoys that travel up and down Kuwaiti highways every day, according to authorities. Security officials said that the men had been under surveillance for some time and that weapons and ammunition were found at the home where they were arrested.

"They were trying to hunt the American Army in the highways," said Col. Ahmad Shergawi, a spokesman for the Interior Ministry. "They had a mission to do something in the highways. . . . We caught them before they did anything."

The arrests further unsettled an already jittery nation that has become a target for supporters of bin Laden because of the heavy U.S. military presence here. In October, a U.S. Marine was killed and another injured in an attack by Islamic gunmen. In November, two U.S. soldiers were shot and wounded by a Kuwaiti traffic policeman. And last month, an American civilian contractor was killed and a second hurt when an al Qaeda supporter ambushed them.

Shocked by the October incident, the Kuwaiti government began cracking down on suspected extremists, rounding up many and putting others under observation. Shergawi said today's arrests resulted from such surveillance.

The suspects were identified as Ahmad Mutlaq Mutairi, 29, Abdullah Mutlaq Nasser Mutairi, 32 and Mussaed Hawran Shbeib Enezi, 28. Shergawi said that the first two are brothers and that Ahmad Mutlaq Mutairi had traveled in 2001 to Afghanistan, where many Arabs trained in al Qaeda terrorist camps or fought alongside the Taliban government.

Troops from the United Arab Emirates arrived Sunday to help defend Kuwait against any retaliation by Iraq. Several U.S. and British schools have closed, and many Western expatriates have fled in anticipation of a war. At hotels where U.S. civilian contractors and journalists are staying, concrete barriers, metal detectors and security officers armed with assault rifles have appeared in recent days.

Each day brings new warnings of Iraqi spies or al Qaeda operatives at work in Kuwait. The Interior Ministry said Sunday that an Iraqi arrested two weeks ago had been sending information about U.S. military forces and their main base, Camp Doha, to Baghdad. A Kuwaiti arrested in January was accused of planning to poison the U.S. military's food supply.

About 100,000 U.S. troops and 13,000 British troops have arrived in Kuwait in advance of a possible attack on Iraq, an especially big force for a country smaller than New Jersey. Highways are clogged by miles-long convoys of military trucks and tanks, guarded by Humvees with machine gunners watching the other traffic. Thousands of U.S. civilians work for the military here providing logistics.