CARACAS, Venezuela – Opposition officials on Wednesday condemned the disappearance and apparent detention of Juan Guaidó’s uncle after the opposition leader returned home this week from a global tour to build support for his effort to oust President Nicolás Maduro.

Guaidó’s uncle, Juan José Márquez, traveled with him on a flight from Lisbon that landed at Simón Bolívar International Airport in Maiquetía shortly after 4:30 p.m. Tuesday. Senior opposition officials said Guaidó last saw Márquez just before he crossed into an arrivals hall, where Guaidó’s supporters clashed with Maduro’s backers, who hurled insults at the opposition leader and appeared to manhandle him as he tried to make his way to a waiting car.

Márquez does not hold an official position in the opposition leadership.

“I hold you responsible, usurper Nicolás Maduro, and each one of your minions in Maiquetía for what happens to Juan José Márquez, an honest and brave man who knows the value of this fight and whose only responsibility is to worry about his family,” Guaidó tweeted Wednesday.

Venezuela’s communications ministry did not respond to a request for comment.

Guaidó, the National Assembly president who is recognized as Venezuela’s rightful leader by the United States and more than 50 other nations, defied a travel ban to spend three and a half weeks in Europe and the United States, lobbying for more international pressure to isolate Maduro and force him from office. The United Nations last year issued a report documenting the torture, arbitrary arrest and killing of government opponents and citizens under Maduro.

Before Guaidó’s return Tuesday, the Trump administration warned Maduro not to harm or detain the leader. The opposition’s U.S. backers quickly decried his uncle’s disappearance.

“Kidnapping interim president @JGuaido’s relatives only demonstrates that the dictatorship is weak and desperate,” tweeted Michael Kozak, the acting assistant secretary of state for Western Hemisphere affairs. “We demand the immediate release of Juan José Márquez unharmed. #Democracy cannot be intimidated, this must stop!”

Romina Botaro, Márquez’s wife, said her husband called her while being held at customs. She said he was wearing a protective vest that he was told he needed to declare.

That was the last she heard from him, she told reporters at a news conference Wednesday. When Márquez’s lawyers went to the airport late Tuesday, she said, they were told he had disappeared from the building.

“We do not know his whereabouts,” she said.

Later Wednesday, opposition lawmaker Delsa Solórzano tweeted, “they inform us that they are transferring Juan Márquez, uncle of the President @jguaido, to court.” Opposition officials said they could not immediately confirm that Márquez had turned up in custody. But they denounced what they said was an attempt by “the Maduro dictatorship” to give him a public defender.

“Juan José Márquez . . . has a private [attorney],” Guaido’s press team tweeted. The Washington Post could not immediately reach attorney Joel García.

Botaro said Márquez, an airline pilot, had nothing to do with politics.

“Like any protective uncle, he only wanted to escort his nephew and protect his safety,” she said.

Guaidó said Maduro had targeted his family.

“Threats have not stopped us or will stop us” he said.

The opposition denounced the arrest of the organizers of Guaidó’s homecoming rally Tuesday evening. Several hundred supporters gathered in eastern Caracas to hear the opposition leader speak. Opposition officials said the drivers of three buses that carried lawmakers to the airport to greet Guaidó were stopped and detained.

Deyalitza Aray, an opposition lawmaker, was held but later released.

“It was an illegal detention, without any sense,” she told reporters Tuesday in Caracas. “This is a dramatic situation because it demonstrates how the regime acts against citizens and the congress.”

The country’s national press union said at least six journalists covering Guaidó’s return were attacked and robbed. Some of them were bitten and punched, the union said.

Maduro’s government has sought to penalize Guaidó’s supporters in recent months. Government forces closed down the hotel and seized the cars he used during at least one campaign stop. Pollster and political analyst Luis Vicente Leon said it was clear Maduro was sending “a message.”

“Politicians, deputies, assistants, many people have been arrested and intimidated,” he said. “And not only people but places have also been closed down. This is a very clear strategy that tries to encircle anything that supports Guaidó.”

Maduro’s message, he said, is that Guaidó’s “fight is expensive, and his uncle is a perfect way to send this message.”