Ten of the 12 defendants charged with plotting to overthrow the Communist government of Laos pleaded not guilty to amended charges Friday in Sacramento, as a federal judge questioned key allegations in the government's case.

They entered the pleas to an amended grand jury indictment issued in June. Like previous indictments, the revised charges allege the men conspired to send fighters and weapons including machine guns and explosives to Southeast Asia to attack Laos.

All 12 remain free after pleading not guilty to earlier indictments dating to 2007, when they were arrested. Another defendant previously pleaded not guilty, while prosecutors are in the process of dropping charges against the 12th.

One defendant is a retired U.S. Army lieutenant colonel, and 11 are members of California's Hmong community, many of whom fought for the U.S. during the Vietnam War.

Besides the 12, charges were dropped last year against Vang Pao, a national Hmong leader and former Laotian general. Prosecutors said they dropped those charges after reviewing translations of more than 30,000 pages of documents and conversations recorded by an undercover agent.

During Friday's hearing, U.S. District Judge Frank Damrell repeatedly questioned whether the government had presented enough evidence or details to support its charges. For instance, he said the indictment fails to back prosecutors' claims that the machine guns and explosives would have been made or shipped through the United States, a key element of the charges.

"You're on thin ice," the judge told prosecutors. "Where the rubber hits the road, there's no evidence where these weapons were coming from."

Damrell also questioned whether the government can prove the 12 violated the Neutrality Act, which prohibits Americans from interfering with foreign governments, because prosecutors are dropping their case against the two men it originally alleged were the ringleaders. Aside from Vang Pao, the government is deferring its prosecution of a second alleged leader, Youa True Vang, and plans to drop the charges next year.

That in effect leaves the government's own undercover agent as the one orchestrating the plot, Damrell said. The weapons at the center of the allegations never existed, Damrell said, except for samples of weapons and explosives shown by the agent himself.

Some evidence is lacking because federal agents hurried to arrest the men before they could carry out the coup, responded Robert Wallace Jr., an attorney with U.S. Justice Department's National Security Division who is assisting local prosecutors with the sensitive case.

However, he and other prosecutors said they can prove their case.

Damrell did not immediately rule on the defense motions.

Even if the judge throws out some of the charges, lead defense attorney Daniel Broderick said it will not end the government's case. Other charges would remain, and the judge could let prosecutors amend any charges he dismisses.

However, Damrell has also scheduled a hearing next spring on a defense request that the entire case be dismissed because of alleged misconduct and misstatements by the undercover federal agent.