An alleged plot to overthrow the communist government of Laos began to unravel almost from the moment it was hatched by Hmong leaders in the United States last winter, according to a federal undercover agent.

Nine Hmong leaders, including a former Laotian military general, and a former officer in the California National Guard were arrested Monday in California during a sweep by more than 200 federal, state and local agents. Federal prosecutors said other arrests could follow.

Authorities acted because weapons shipments were set to begin this month to areas in Thailand along the Laotian border, according to a criminal complaint filed in U.S. District Court in Sacramento. The buildup was in preparation for a coordinated set of mercenary attacks that investigators said were designed to kill communist officials and destroy government buildings, the complaint said.

Among the nine were former Laotian Gen. Vang Pao, a prominent Hmong leader who lives in Orange County, and former California National Guard Lt. Col. Harrison Ulrich Jack, a 1968 West Point graduate and Vietnam War veteran.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives was in on the plot almost from the beginning, after the agency was tipped by a Phoenix-area arms dealer. The dealer told federal agents that Jack had approached him seeking to buy 500 AK-47 automatic weapons, according to a sworn affidavit by the agent. The agent's name was redacted from court records.

On Feb. 7, the agent said he secretly recorded his luncheon meeting with Jack, Vang Pao and 10 associates at a Thai restaurant a few blocks from the state Capitol in Sacramento. They then walked to a recreational vehicle parked nearby to examine machine guns, grenade launchers, anti-tank rockets, anti-personnel mines and other weapons.

On Feb. 15, Jack called the agent to report that the plot was "in motion," according to the affidavit. Hmong leaders had agreed to buy $9.8 million worth of military weapons, Jack said in a recorded conversation, with much of the money coming from immigrants throughout the United States.

"We're looking at conspiracy to murder thousands and thousands of people at one time," Assistant U.S. Attorney Bob Twiss said in federal court Monday.

He said thousands of coconspirators remain at large, many in other countries. Prosecutors said they believe all the leaders of the plot are in custody.

Members of Laos' ethnic Hmong minority were recruited in the 1960s by the Central Intelligence Agency to fight on behalf of a pro-American government, but they were all but abandoned after communists took over Laos in 1975. More than 300,000 Laotian refugees, mostly Hmong, fled into Thailand. Most later resettled in the United States and elsewhere.

The permanent secretary for the Lao Ministry of Foreign Affairs, Somphet Khoukahoun, said Tuesday the government would not comment until it is officially informed of the plot by the U.S. government.

The government of Thailand had been informed but doesn't plan to comment before a verdict, Tharit Charungvat, a spokesman for the Foreign Affairs Ministry, said in Bangkok. "However, we would like to insist that Thailand will not tolerate the use of its territory for any movement that undermines the stability of its neighboring countries," he said.

Vang Pao, now 77, led CIA-backed Hmong forces in Laos in the 1960s and 1970s as a general in the Royal Army of Laos. He emigrated to the U.S. about 1975 and has been credited by thousands of Hmong refugees with helping them build new lives in the U.S.

Hmong leaders in Thailand said they found the charges unbelievable. "I don't believe Gen. Vang Pao planned to cause trouble in Laos. I think the charges are meant by rival Hmong in the United States to smear him," said Ming Wui, a Hmong Christian minister in Thailand's Phetchabun province.

The seven others charged were all prominent members of the Hmong community from California's Central Valley. All nine are charged with violating the federal Neutrality Act and face the possibility of life in prison.

"No matter how strongly held their beliefs, citizens of the United States cannot become involved in a plot to overthrow a sovereign government with which the United States is at peace," Drew Parenti, FBI special agent in charge of the Sacramento region, said during a news conference following the defendants' initial court appearance.

Another suspect, Nhia Kao Vang of the Sacramento suburb of Rancho Cordova, was arrested later Monday based on information obtained from the others.

U.S. Magistrate Judge Kimberly J. Mueller ordered the defendants held until separate hearings later this week.

Attorneys representing the defendants who appeared in federal court Monday declined to comment.

The defendants acted through the Lao liberation movement known as Neo Hom, led in the U.S. by Vang Pao. It conducted extensive fundraising, directed surveillance operations and organized a force of insurgent troops within Laos, according to the complaint.

As recently as May, people acting on behalf of the committee were gathering intelligence about military installations and government buildings in the Laotian capital of Vientiane, according to prosecutors. The defendants had gone so far as to issue "an operations plan" to a contractor who was to conduct a military strike in the city and reduce government buildings to rubble, the complaint alleged.

Jack acted as the negotiator between the Hmong leaders and the undercover agent, according to court records.