Venezuelan opposition leader Maria Corina Machado said her opposition colleague Juan Pablo Guanipa had been kidnapped just hours after being released from detention.
The Nobel Peace Prize winner said on Sunday that Guanipa, leader of the Justice First party, was taken in the Los Chorros neighbourhood of the capital Caracas.
"Heavily armed men dressed in civilian clothes arrived in four vehicles and took him away by force," she wrote on social media early on Monday.
A former vice-president of the National Assembly, Guanipa spent eight months in prison and was among several political prisoners released since the US seized Venezuela's then-President Nicolas Maduro in January.
His centre-right party said Guanipa had been kidnapped by the "repressive forces of the dictatorship" while he was moving between locations.
