MEXICO CITY -- The U.S. Department of State has demanded the release of Bishop Rolando Álvarez of Matagalpa and other imprisoned Nicaraguan religious leaders following a wave of detentions targeting Catholic clergy over the Christmas season.

The Jan. 2 statement described Bishop Álvarez and the other religious leaders -- including Bishop Isidoro Mora of Siuna -- as "unjustly detained" and deplored the conditions in which they were being held. Bishop Álvarez has been held for more than 500 days.

"Nicaraguan authorities have kept Bishop Álvarez in isolation, blocked independent evaluation of the conditions of his imprisonment, and released staged videos and photographs that only increase concerns about his well-being," read the statement, signed by State Department spokesperson Matthew Miller.

The regime of President Daniel Ortega and his wife, Vice President Rosario Murillo, "continues to impose severe restrictions on religious communities and deny Nicaraguan citizens the ability to freely practice their religions and express their beliefs. We once again call on the Nicaraguan government to release Bishop Rolando Álvarez immediately and without conditions."

In a separate post on social media platform X, formerly Twitter, Miller called Bishop Álvarez's detention "unconscionable," adding, "Freedom of belief is a human right."

At least 13 priests -- mostly in the Archdiocese of Managua -- were detained between Dec. 26 and Dec. 31, according to exiled Nicaraguan lawyer Martha Molina, who has tracked attacks on the Catholic Church in Nicaragua. Many were taken from their parish residences by police and paramilitaries.

The Nicaraguan government -- seemingly responding to the U.S. statement -- released photos Jan. 2 of Bishop Álvarez receiving medical attention from a prison doctor.

Dressed in a pink dress shirt and gray slacks, Bishop Álvarez appeared pale and gaunt as a physician took his blood pressure and performed tests. A government statement claimed the bishop's "vital signs are fine" after being seen by an internal medicine specialist.

The government has released photos of Bishop Álvarez from time to time -- visiting with two siblings or receiving medical attention -- but the state of his health is unknown.

Church observers have expressed concern for the wellbeing of the arrested priests, whose status as detainees remains unknown. Bianca Jagger, the Nicaraguan human rights activist, said on X that she received information that "one of the priests that they kidnapped was transferred to the hospital. I demand proof of life."

Pope Francis expressed concern for Nicaragua and the captive priests Jan. 1 at his New Year's Angelus prayer.

"I have been following with deep concern what is happening in Nicaragua, where bishops and priests have been deprived of their freedom."

The pontiff expressed his "closeness in prayer" to the detained priests and their families, "and to the entire church in the country."

"I hope that we will always seek the path of dialogue to overcome difficulties. Let us pray for Nicaragua today."

Dialogue has proved difficult in Nicaragua, despite church efforts to assume a mediating role after protests erupted in 2018 -- with demonstrators demanding the ouster of President Daniel Ortega and his wife, Vice President Rosario Murillo. Priests provided shelter for protests and later accompanied the families of political prisoners, even as their parishes were besieged by pro-regime police and paramilitaries.

The calls for action on Bishop Álvarez and the detained clergy come as the regime crushes even the most minimal dissent in the country -- which analysts have described as turning increasingly tyrannical and totalitarian.

Clergy in the country are often spied upon and paid visits by police and paramilitaries in acts of intimidation and to deliver orders -- such as the suspension of acts of popular piety and public processions on feast days.

Offering prayers for the imprisoned can land clergy in trouble. Bishop Isidoro Mora was detained Dec. 20, along with two seminarians, following the celebration of a Mass in the city of Matagalpa, where he offered spiritual support for Bishop Álvarez -- the local leader.

On Dec. 31, Cardinal Leopoldo Brenes of Managua urged prayer for the "families and communities that at this moment feel the absence of their priests or are experiencing other types of pain."

Molina has counted more than 770 attacks on the Catholic Church in Nicaragua since 2018 – with 2023 registering the most incidents. Previously detained priests have routinely been sent into exile -- spare Bishop Álvarez, who has refused to abandon Nicaragua, despite imprisonment.

Motives for the mass detentions of priests remain unknown. Murillo, the government spokeswoman, did not respond to a request for comment.

Exiled Nicaraguan journalist Emiliano Chamorro posited on X that the regime could be pushing for a change in church leadership through the appointment of bishops it considers friendlier.

Molina didn't discard the theory, but told OSV News, "I don't see priests in the Catholic Church who are complicit with the regime and could be elevated to bishops."

Molina added, "The dictatorship may be preparing a massive exile to achieve its proposed objective, which is to eradicate the Catholic Church from Nicaragua. … (Priests) speak the truth and they don't want to hear it."

Papal biographer Austen Ivereigh wrote on X on Jan. 1 that "A dictatorship suppressing the Church causes the Church to grow stronger and hastens the end of the dictatorship."

He added: "It's the iron law of history every Latin American dictator chooses to forget."