CARACAS (Reuters) - Venezuelan authorities detained opposition leader Juan Guaido's uncle after the two men arrived at the main airport in Caracas, ruling Socialist Party Vice President Diosdado Cabello said on Wednesday.

Juan Jose Marquez, who was with Guaido on his return to Venezuela on Tuesday after a three-week international tour, passed "migration normally, and as he was about to leave ... he was held for an alleged Seniat review," Guaido's press team wrote on Twitter. Seniat is Venezuela's national tax agency.

"He's detained, not forcibly disappeared, he's detained for bringing prohibited substances onto a flight," said Cabello on his weekly television program Wednesday evening.

He then showed pictures of a bulletproof vest and alleged explosive material he said belonged to Marquez, and said Marquez had also brought in an electronic file containing information about "operations against Venezuela."

Marquez's wife, Romina Botaro, said her husband was an airplane pilot who had nothing to do with politics.

Opposition lawmaker Delsa Solorzano said that Marquez's hearing began Wednesday night in a court by the airport just outside Caracas, and that he is being represented by private lawyers.

Cabello said Marquez would not be released. He also showed a photo of Guaido's Venezuelan ID card cut up, saying it had been confiscated at the airport.

President Nicolás Maduro "is a coward ... who does not show his face, who does not dare to step in a public square without security ... he mounts an attack against my family," Guaido told reporters on Wednesday morning before a session of the opposition dominated National Assembly.

The Ministry of Communication did not respond to a request for comment.

At the airport, Guaido was met by supporters as well as pro-government agitators who pushed and shouted insults at him and attacked journalists, photographers and opposition lawmakers, according to Reuters witnesses.

Guaido, who is recognized by more than 50 countries as Venezuela's legitimate president, hopes to revive the inertia of 2019 when he led a groundswell of protests against Maduro.

Venezuela's economic collapse under Maduro has prompted nearly 5 million people to emigrate, creating a migration crisis in nearby Latin American nations.

Maduro calls Guaido a U.S-backed puppet who seeks to oust him in a coup.

(Reporting by Sarah Kinosian, Deisy Buitrago, Vivian Sequera and Brian Ellsworth; Writing by Sarah Kinosian; Editing by Richard Chang, Grant McCool and Gerry Doyle)