Venezuelan opposition leader María Corina Machado said on Monday one of her closest allies was kidnapped hours after being released from prison.

The government had released several prominent opposition members from prison on Sunday after lengthy politically motivated detentions.

Machado said on social media that Juan Pablo Guanipa was taken around midnight in a residential neighbourhood of the capital, Caracas.

“Heavily armed men, dressed in civilian clothes, arrived in four vehicles and violently took him away,” she posted on X. “We demand his immediate release.”

Guanipa, a former governor, had told reporters hours after his release: “I am convinced that our country has completely changed. I am convinced that it is now up to all of us to focus on building a free and democratic country.”

Guanipa had spent more than eight months in custody.

Alfredo Romero, president of Venezuelan-based prisoners’ rights group Foro Penal, expressed serious concern about Guanipa’s disappearance. “So far, we have no clear information about who took him,” he said on X. “We hope he will be released immediately.”

Foro Penal confirmed the release of at least 30 people on Sunday.

The releases of the opposition figures came as the government of acting president Delcy Rodríguez has faced mounting pressure to free hundreds of people whose detentions months or years ago have been linked to their political activities. The releases also followed a visit to Venezuela by representatives of the UN High Commissioner for Human Rights.

The government’s press office did not immediately respond to a request for comment early on Monday.

Rodríguez was sworn in as Venezuela’s acting president after the 3 January capture of then-President Nicolás Maduro by the US military. Her government began releasing prisoners days later.

Some of those freed on Sunday joined families waiting outside prisons for their loved ones to be released. They chanted “We are not afraid! We are not afraid!” and marched a short distance.

In addition to Guanipa, Machado’s political organisation said several of its members were among the released, including María Oropeza, who livestreamed her arrest by military intelligence officers as they broke into her home with a crowbar. Machado’s attorney, Perkins Rocha, was also freed.

Guanipa’s son, Ramón, said on social media that his father was “intercepted and kidnapped” by “a group of approximately 10 unidentified people.” He also described three vehicles involved in the situation.

“We demand proof of life immediately and his release,” Ramón Guanipa wrote on X.

Guanipa was detained in May last year and accused by the interior minister, Diosdado Cabello, of participating in an alleged “terrorist group” plotting to boycott that month’s legislative election. Guanipa’s brother Tomás rejected the accusation, and said the arrest was meant to crack down on dissent.

“Thinking differently cannot be criminalised in Venezuela, and today, Juan Pablo Guanipa is a prisoner of conscience of this regime,” Tomás Guanipa said after the arrest.

Rodríguez’s government announced on 8 January it would free a significant number of prisoners – a central demand of the country’s opposition and human rights organisations with backing from the US – but families and rights watchdogs have criticised authorities for the slow pace of the releases.