Chavez's warning came hours after his vice president, Jose Vicente Rangel, accused officials at the U.S. Embassy of involvement in a spying case involving several Venezuelan naval officers who allegedly passed sensitive information to the Pentagon.

Chavez focused his speech to thousands of activists on summoning a global "battle" to resist what he termed U.S. imperialism.

The frequent and vocal critic of U.S. global policy used especially harsh terms to describe the U.S. government, calling it a "perverse, murderous, genocidal, immoral empire."

He addressed the spying accusations for the first time since the allegations came to light earlier this week.

"We've just discovered a case, one more espionage case," Chavez told the audience of activists who are attending the World Social Forum in Caracas this week.

"I warn the U.S. government: the next time we detect a soldier or civilian official - but above all American soldiers - trying to obtain information about our armed forces, we're going to put them in prison."

Chavez has repeatedly accused the U.S. government of spying and plotting to oust him, while U.S. officials have firmly denied the allegations.

The latest accusations have brought new tension to an already rocky relationship between Washington and Chavez's government.

The U.S. Embassy declined comment on Rangel's remarks Friday. The U.S. State Department has called the allegations an internal matter for the Venezuelan government.

In his speech at a Caracas coliseum, Chavez called for activists to form "a great international anti-imperialist front to do battle in the entire world."

"The battle must be waged in the entire world. We have to link all of our causes - unity," Chavez said.

Activists chanted Chavez's name when he entered the arena. They held a banners reading "No to imperialism" and another with an image of Cuban revolution leader Che Guevara.

Chavez waved to the throng and blew kisses to the assembly, timed to coincide with the annual market-friendly World Economic Forum in Davos, Switzerland.

Washington has raised concern about the health of democracy under Chavez and has accused him of destabilizing the region. Chavez has shrugged off the claims, saying his government is democratic and it is the U.S. that is a destabilizing force.

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