Two nephews of Venezuela's powerful first lady, arrested in Haiti on charges of conspiring to smuggle 800kg of cocaine into the US, will be arraigned in New York on Thursday.

Coming just three weeks ahead of key Venezuelan legislative elections, the arrests are likely to exacerbate already tense relations between Washington and Caracas - and cast a hard look at US accusations of drug trafficking at the highest levels of embattled President Nicolas Maduro's socialist administration.

The two suspects, Efrain Campos and Francisco Flores, were extradited from Haiti and will be arraigned in a federal court, said a US law enforcement official who insisted on anonymity because he wasn't authorised to discuss the case.

Michael Vigil - a former head of international operations at the Drug Enforcement Administration, who was briefed by US authorities about the lengthy undercover operation that led to the arrests, said Campos and Flores were arrested in Haiti's capital, Port-au-Prince, after arriving from Venezuela aboard a private plane.

Both men were carrying diplomatic passports, even though they don't have diplomatic immunity, Vigil said.

'First Combatant'

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He also said Campos had claimed to law enforcement that he is the son of Venezuela's first lady Cilia Flores and stepson of Maduro.

Another person briefed on the incident, who agreed to talk about the case only if not quoted by name, said Campos is the son of a deceased sister of Flores and was partly raised by the first lady and Maduro.

Cilia Flores, who Maduro calls the "First Combatant", is one of the most powerful members of Venezuela's revolutionary government and a constant presence alongside her husband whenever he appears in public.

The two travelled this week to Saudi Arabia for a summit and she's expected to be with the president on Thursday, when he's scheduled to address the United Nations Human Rights Council at a special meeting in Geneva called at Venezuela's request.

Source: AP