Spain's former prime minister met in jail with Venezuelan opposition leader Leopoldo Lopez on Saturday, the first meeting of its kind in the more than two years since his imprisonment for inciting violence during anti-government protests.

Jose Luis Rodriguez Zapatero's surprise prison visit is part of a high-risk diplomatic effort to defuse the escalating crisis in Venezuela, where President Nicolas Maduro is under pressure to negotiate an end to a stalemate with the opposition, which is seeking his ouster amid triple-digit inflation and widespread food and medicine shortages.

Adriana Lopez, Lopez's sister, told The Associated Press that the meeting lasted about 90 minutes. She said she didn't know what the two discussed and declined further comment.

It's the first time an outside visitor besides Lopez's family or lawyers have met with the combative leader in the military prison outside Caracas where he's being held. In 2015, he was sentenced to nearly 14 years in jail in proceedings widely condemned as a politically-motivated show trial by the U.S. and human rights groups.

"We don't know who permitted it or why," Leopoldo Lopez, who shares his son's name, said on Twitter. "All we know is that there was a surprise."

Venezuela's opposition is demanding the release of Lopez and dozens of other activists it considers political prisoners as part of an international mediation effort led by Zapatero and the former presidents of Panama and the Dominican Republic.

Last month, the three presided over two days of informal meetings in the Dominican Republic in which they shuttled messages between representatives of the opposition and the government.

One of the government's participants at that meeting, Caracas Mayor Jorge Rodriguez, escorted Zapatero to the jail on Saturday but did not partake in the meeting, according to a source close to the family who spoke on condition of anonymity because the conversation was private.

Zapatero has kept quiet about his dealings and many observers believe they are doomed to fail so long as Maduro refuses to yield to the opposition's demands that his government allow to go forward this year a proposed recall referendum on whether to cut short his six-year term.

But Saturday's meeting is likely to give more oxygen to the mediation effort, which has the support of the Obama administration and regional governments and comes as pressure is mounting on the Organization of American States to suspend Venezuela for violating standards of democracy and the rule of law.

Lopez's jailers have in the past turned back attempted visits by the former leaders of Colombia and Chile, as well as legislative delegations for from Brazil and Spain.

Venezuela's government has yet to comment.

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Hernandez reported from Bogota, Colombia. AP Writer Joshua Goodman contributed to this report from Lima, Peru.