A TV frame grab from Venezuelan Vice President Nicolas Maduro's announcement of Chavez's death. (AP Photo/Telesur)

Venezuelan President Hugo Chavez had been fighting cancer for two years when he died this afternoon at age 58, but some Venezuelans -- including new President Nicolas Maduro -- are convinced foul play is to blame.

Maduro promised on state television that a "scientific commission" would look into Chavez's death and the possibility that his "historical enemies" had somehow induced his disease, reported El Diario. On social media and in several news outs, that "historical enemy" was interpreted as the United States.

"There have been historical cases, too many historical cases" of such clandestine assassinations, Maduro said, invoking the conspiracy theories around the death of Palestinian leader Yasser Arafat.

Chavez made similar allegations against the U.S. government in 2005.

"If they kill me, the name of the person responsible is George Bush," he said.

The State Department has forcefully disavowed the accusations against the U.S. in general, and against two officials who were expelled from Venezuela for espionage earlier this afternoon.

"An assertion that the United States was somehow involved in causing President Chavez's illness is absurd, and we definitely reject it," State Department spokesman Patrick Ventrell said. "The United States has options of reciprocal action available to it under the Vienna Convention on Diplomatic Relations."

The theory does not seem to be gaining much ground in Venezuelan Twitter circles, either.

"These people promote the crazy thesis of Chavez's assassination!" wrote one man. "Since it's not epic that the guy died in his bed."

"Yes, the U.S. caused Chavez's cancer, the Russian meteor, the bird flu, and the sinking of the Titanic," wrote another in Chile.

Maduro's allegations have, however, received a boost from Eva Golinger, the prominent Venezuelan lawyer and editor who, in an interview with Russia Today, claimed that there was concrete evidence for Chavez's assassination. Videos and articles of that interview -- like this one, from Venezuela's UltimasNoticias.com -- have been widely circulated on Twitter.

"There is evidence that 70 years ago they tried to assassinate then Cuban President Fidel Castro with radiation, in addition to other methods," Golinger said in an interview. "We can only imagine the weapons capacity the U.S. possesses today."

See TIMELINE: The life and rule of Hugo Chavez

HUGO CHAVEZ, in photos