BOGOTA -- Venezuelan President Hugo Chavez's plans to acquire high-performance aircraft and submarines, including from Russia, are viewed by Washington as destabilizing to the region, the top US military chief said Thursday.

Admiral Michael Mullen, the chairman of the Joint Chiefs of Staff, said the United States was greatly concerned about a Venezuelan military buildup that has been accompanied by strong anti-American rhetoric on Chavez's part.

He pointed to "what Mr. Chavez has done militarily in recent years and his acquisitions -- both those he's made as well as those he states he's making for the future -- high performance airplanes, modern submarines."

Chavez is negotiating with Russia to buy five diesel electric submarines that he says Venezuela needs to protect its extensive offshore oil drilling facilities.

He also went shopping in Belarus in June for an air defense system.

And in 2006, Venezuela signed contracts with Russia to buy 53 Mi-24 armored helicopter gunships, Sukhoi 30 fighter planes and 100,000 Kalashnikov rifles.

The Venezuelans also have talked about building a factory to manufacture the AK-47 assault rifles in Venezuela, a development that US and Colombian officials fear could flood the region with arms.

"To the degree these capabilities come into the theater," Mullen said, "they are a great concern -- not just to Colombia, which has been expressed, but to the region, and in fact very much to the United States."

"And to the degree they arrive in theater, I believe they will have a destabilizing effect as opposed to trying to create stability," he said.

Mullen spoke at a news conference with Colombia's Defense Minister Juan Manuel Santos and Armed Forces Chief General Freddy Padilla at the outset of a two-day visit.

Colombian President Alvaro Uribe has taken a dim view of Chavez's intentions, accusing him of supporting Colombia's main rebel group, the FARC, and rejecting his call for it and the ELN rebel group to be removed from the US list of terrorist organizations.

Venezuela's National Assembly on Thursday backed Chavez call issuing a resolution describing Colombia's FARC and ELN rebels as "belligerents" who should be dealt with "in a political framework."

Asked whether Venezuela was supporting the rebels, Mullen said the United States is concerned about it, but added: "I am not aware of any specific support Mr. Chavez has provided the FARC."

Chavez was instrumental in securing the release on January 10 of two political hostages held by the FARC, who are still holding 45 other prominent hostages, including three American defense department contractors captured after their plane crashed near a FARC camp in February 2003.

Unconfirmed local press reports said the FARC was preparing to release three more hostages, possibly including one of the Americans, but Santos said he had no official word of any movement.

If the FARC says it will release them, and the Red Cross agrees to mediate the transfer, Santos said "we of course are going to collaborate, as we have in the past."

The visit came just a day after Chavez accused the United States and Colombia of engaging in a plot to kill him, claiming he had evidence to support it.

Both Mullen and Santos brushed off the charge, saying there had been many other claims like it before.

"From the United States' perspective, they are unfounded accusations," said Mullen, adding that charges by Chavez of US plots to assassinate him have "been out there for a long time."

"In that regard, we really, from the United States' perspective, don't pay that much attention to it," he said.

Santos said: "He should show the evidence, and if it is true we will take appropriate action."