MANAGUA (Reuters) - The Nicaraguan government said on Thursday a man arrested in May last year during months of anti-government protests was killed in a shooting at the prison near Managua where he was being held.

The prisoner, Eddy Montes, was a U.S. citizen, his cousin Paola Montenegro told Reuters, after Nicaraguan media published photos of what appeared to be his U.S. passport.

The U.S. embassy in Nicaragua condemned the use of lethal force against Montes, calling him a political prisoner in a post on social media. It demanded that the circumstances of the incident are fully investigated.

The Nicaraguan interior ministry had said in an earlier statement Montes had family who were of foreign nationality but gave no further detail.

Hundreds of people were killed and hundreds more detained in a crackdown on protests that were triggered in April last year by a social security reform but quickly swelled into a national call to oust President Daniel Ortega.

Montes was part of a group of prisoners that tried to snatch a gun from a guard while the International Red Cross was visiting the prison, the interior ministry said. The guard acted in self-defense, it said.

Montes had been accused of attacking a police station during last year’s protests.

The Nicaraguan government has said it would release all people arrested during the protests as a step to restart dialogue with opposition groups. It said last month it had released more than 600 prisoners, but others remain in custody.