Hours before Venezuelan President Hugo Chavez died, his second-in-command accused enemies of giving him cancer and announced the expulsion of two U.S. diplomats for an alleged plot to destabilize the government.

"There's no doubt that Commandante Chavez's health came under attack by the enemy," Vice President Nicolas Maduro said in an address to the nation from the presidential palace.

The old enemies of our fatherland looked for a way to harm his health," according to Maduro, drawing a parallel to the illness and 2004 death of Palestinian leader Yasser Arafat, which some supporters blamed on poisoning by Israeli agents.

He said a special commission would investigate how Chavez, 58, ended up with the unspecified cancer that months of chemotherapy and radiation and four surgeries failed to tame.

State Department spokesman Patrick Ventrell said in a statement it was "absurd" to suggest that the U.S. was somehow involved in Chavez's illness.

The allegation was made against a backdrop of diplomatic tension, with Caracas announcing that two American Air Force attachés had been given 24 hours to leave the country.

Maduro accused one of them, David Delmonaco, of spying and meeting with Venezuelan military officials for nefarious purposes. The expulsion of the second, Devlin Kostal, was announced soon after.

Defense Department spokesman Lt. Col. Todd Breasseale said Delmonaco would be leaving Caracas and that Kostal was already in the U.S. and denied the allegations against them.

"We completely reject the Venezuelan government's claim that the United States is involved in any type of conspiracy to destabilize Venezuela government," he said.

Ventrell also dismissed the accusations.

"Notwithstanding the significant differences between our governments, we continue to believe it important to seek a functional and more productive relationship with Venezuela based on issues of mutual interest," he said.

"This fallacious assertion of inappropriate U.S. action leads us to conclude that, unfortunately, the current Venezuelan government is not interested in an improved relationship."

Venezuela's relations with the U.S. have been strained for years, and Chavez saw conspiracies everywhere.

In 2008, he expelled the American ambassador, claiming the U.S. was orchestrating a military coup. He had repeatedly claimed to be the target of assassination plots from domestic and international opponents.

NBC News' Havana bureau chief Mary Murray, the Associated Press and Reuters contributed to this report