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

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

Machado said on social media that Juan Pablo Guanipa was taken around midnight in a residential neighborhood 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."

The releases of the opposition figures came as the government of acting President Delcy Rodriguez 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 of representatives of the U.N. High Commissioner for Human Rights.

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

Rodriguez was sworn in as Venezuela's acting president after the Jan. 3 capture of then-President Nicolas Maduro by the U.S. military. Her government began releasing prisoners days later.

Some of those freed 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.

"I am convinced that our country has completely changed," Guanipa, a former governor, had told reporters hours after his release. "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.

Venezuelan-based prisoners' rights group Foro Penal confirmed the release of at least 30 people Sunday.

In addition to Guanipa, Machado's political organization said several of its members were among the released, including Maria 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.

Alfredo Romero, president of Foro Penal, expressed serious concern over 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."