Several Russian and international media outlets have reported about Russian mercenaries sent to Venezuela to help Maduro who is under international pressure to hold elections.

Asked on television about whether there were "400 of our fighters protecting Maduro" in Venezuela, Kremlin spokesman Dmitry Peskov responded: "No of course not."

The Russian ambassador to Caracas also dismissed reports of Russian mercenaries in Venezuela.

On Friday, a self-proclaimed Cossack leader close to army veterans said a private military contractors group recently returned from Gabon had "urgently" got together "400 people" to send to Caracas via Cuba.

Yevgeny Shabayev, leader of a local chapter of a paramilitary group of Cossacks, said he had been contacted by relatives of the men because the objectives of the mission to Venezuela were "not clear".

Maduro is under pressure to hold elections after the United States, Canada and some South American governments recognised opposition rival Juan Guaido as acting president.