The government said in a statement that the bishop had “persisted in his destabilizing and provocative activities.” It did not elaborate or say what legal charges the Catholic leader was facing. Two weeks ago, police surrounded his residence, saying he was under investigation for allegedly sponsoring violent anti-government groups, a charge he denies. The government’s spokeswoman, Rosa Murillo — Ortega’s wife and vice president — did not respond to a message seeking comment.

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In the past year, Ortega’s government has jailed nearly all his best-known opponents, including seven politicians who had been expected to seek the presidency last November. His government has also shut down hundreds of civil society groups, as well as universities and media organizations, in one of the most intense waves of repression in the hemisphere.

It has engaged in an increasingly bitter feud with religious leaders in the majority-Catholic country, closing eight Catholic radio stations and expelling the Vatican’s ambassador, the Rev. Waldemar Sommertag. Authorities also expelled 18 nuns from the Missionaries of Charity, founded by Mother Teresa, who had been helping run shelters and orphanages.

Relations between Ortega and the church soured after the government cracked down on nationwide protests in 2018, prompting street battles that left more than 360 dead, according to human rights groups. When Catholic bishops called for justice, the Ortega government accused them of fomenting a coup. Several priests and a prominent bishop, Silvio Báez of Managua, have gone into exile.

Álvarez, 55, has recently been the most influential Catholic critic of the government, speaking out in radio and newspaper interviews about what he has condemned as Ortega’s authoritarian behavior. After his arrest, the archdiocese of Managua said his physical condition had deteriorated but “his courage and spirits are strong.”

U.N. Secretary General António Guterres is “very concerned by the severe closure of democratic and civic space in Nicaragua and recent actions against civil society organizations, including those of the Catholic Church,” a deputy spokesman told journalists on Friday after the bishop’s arrest. He called on the Nicaraguan government to guarantee “freedoms of association, thought, conscience, and religion, and to release all people arbitrarily detained.”

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Government critics said Álvarez’s detention was stunning even by the standards of a country whose democracy had shriveled.

“With a pained, indignant heart I condemn the nighttime kidnapping of Monsignor Álvarez,” tweeted Báez, who is living in the United States. “Once again, the dictatorship has surpassed even its own evil and its diabolical spirit.”

Pope Francis has not commented publicly on the bishop’s detention or any other recent government moves against the Catholic Church, to the dismay of some Latin American human rights activists. The Vatican’s permanent observer to the Organization of American States, Monsignor Juan Antonio Cruz Serrano, expressed concern this month about the developments and called for dialogue.

Ortega, 76, helped lead the Marxist Sandinista revolution that triumphed in 1979, toppling the U.S.-backed Somoza dictatorship. He headed the government until 1990, and then returned to power in 2007. Last year, he won an election after eliminating all possible opposition. Human rights organizations say his government has detained more than 160 political prisoners.

The United Nations estimates that more than 120,000 Nicaraguans have fled the country since 2018, the largest exodus since the civil war of the 1980s.

Álvarez himself left the country during the civil war, moving to Guatemala, where he studied for the priesthood. In 2011, he was named bishop of Matagalpa, one of the least developed areas in Nicaragua. In 2015, he led major demonstrations against government plans to allow mining in a northern area of the country, charging that it would pollute the groundwater. The government backed off.

The bishop “went on horseback to the most remote parts of the mountains to visit the sick and celebrate Mass,” said Emiliano Chamorro, a journalist who accompanied him on several trips. “People love him. He’s a true pastor.”