President Hugo Chavez said Venezuelan authorities have detained an American man and are interrogating him, suspecting he could be a "mercenary" plotting to destabilize the country if the opposition loses the upcoming presidential election.
Chavez told reporters on Friday that under questioning the man said he had been a U.S. Marine.
"The man has military training and he refuses to give information. That in itself is suspicious," Chavez said on state television.
Chavez did not identify the man nor detail the accusations against him. But the case has the potential to ratchet up longstanding tensions between Venezuela and the U.S. less than two months ahead of Venezuela's presidential election.
Chavez said the man was detained while crossing into Venezuela from Colombia on a bus in the middle of the night. He said the American had entered the country illegally.
Chavez announced the man's Aug. 4 arrest on Thursday night, saying he was carrying a U.S. passport with entrance and exit stamps from countries including Iraq, Afghanistan and Libya.
A U.S. State Department official, who spoke on condition of anonymity because he wasn't authorized to speak publicly, said the U.S. government had not been notified of the arrest by the Venezuelan government.
He said that if the detained man is in fact a U.S. citizen, American officials expect "Venezuela will uphold its obligations under the Vienna Convention on Consular Relations and grant U.S. consular officials access to any detained U.S. citizen without delay."
Chavez instructed his justice minister, Tareck El Aissami, to make contact with U.S. authorities to inform them of the case. He said the detained man "has all of his human rights guaranteed."
Chavez said that when the man was detained at a National Guard post in southwestern Tachira state, he tore up part of a notebook that he had with him.
"He has all the appearance of a mercenary," Chavez said at a campaign rally on Thursday. "We are interrogating him."
Chavez suggested, without offering evidence, that the American might have been recruited by government opponents to instigate violent protests if opposition presidential candidate Henrique Capriles loses the Oct. 7 election.
Opposition lawmaker Pedro Pablo Alcantara scoffed at the president's allegations that government foes would attempt to stir up trouble if Chavez is re-elected to a new six-year term.
Alcantara accused the government of encouraging violence against its adversaries in the past while backing groups that have attacked opposition marches.
"It's the president who has promoted violence," he said.
Chavez has repeatedly accused the U.S. government of plotting against him during the past decade, though he usually has provided few specifics of such claims.
The U.S. Embassy in Caracas has been without an ambassador since July 2010. Chavez rejected the U.S. nominee for ambassador, Larry Palmer, accusing him of making disrespectful remarks about his government. That led Washington to revoke the visa of the Venezuelan ambassador.