Venezuela has blocked two ex-presidents from visiting opposition leaders jailed on charges of inciting violence against the government.
Andres Pastrana of Colombia and Jorge Quiroga of Bolivia were not allowed to visit opposition leader Leopoldo Lopez and former mayor, Daniel Ceballos.
Both prisoners started a hunger strike around a week ago.
State officials said the ex-presidents were part of an hostile campaign against the country.
President Nicolas Maduro has said Venezuela's judiciary is independent and those in jail are criminals.
However, their supporters and rights groups say the two men's imprisonment is politically motivated and accused Mr Maduro of cracking down on his opponents.
Mr Lopez is being held in the Ramo Verde military prison outside Caracas, while Mr Ceballos is in a civilian prison in the central state of Guarico.
The presidents attempted to visit both sites.
Leopoldo Lopez is on trial for inciting violence during three months of protests against the government of President Maduro during which 43 people died including some police officers.
Daniel Ceballos, who was mayor of the western city of San Cristobal near the border with Colombia, which was a focus of many of the protests, is accused of supporting street blockades and calling for violence at the protests.
Last month a group of former world leaders sent an open letter to the Venezuelan government urging the release of the opposition leaders.
In April a former Spanish prime minister, Felipe Gonzalez, who announced his intention to help in the legal defence of Leopoldo Lopez, was also denied access to him.
The Venezuelan attorney general said under the country's law Mr Gonzalez could not form part of Mr Lopez's legal team.
Mr Maduro has been scathing about international support for Venezuelan opposition leaders.
"In general, these former prime ministers are usually discredited. They don't even want them in their own countries and then they come over here to disturb us."