Nicaraguan pro-government forces launched an operation in the country's south that left at least 10 people dead and around 20 injured on Sunday, a human rights group said. The dead included six civilians --- among them two children -- and four police, according to the Nicaraguan Association for Human Rights (ANPDH).

The operation by police and paramilitaries targeted the city of Masaya, the nearby Niquinohomo and Catarina communities and the Monimbo neighborhood.

"This is a preliminary report," said ANPDH head Alvaro Leiva, adding that the names and ages of the deceased were still being investigated.

Get Breaking News Delivered to Your Inbox

"There are sharpshooters located in different parts of the city. We ask the citizens to take shelter in their homes," said Leiva.

Residents and rights groups had earlier said that troops used mechanical shovels in the early hours of the day to clear barricades in at least three areas.

"They are going to destroy Masaya, it is absolutely surrounded," Vilma Nunez, president of the Nicaraguan Center for Human Rights (CENIDH), told AFP.

"We are being attacked by the National Police and paramilitaries armed with AK-47s and machine guns in our indigenous neighborhood of Monimbo," said Alvaro Gomez, a resident. "We are resisting with homemade bombs and stones."

Leiva addressed an urgent call for help to the bishops of the Episcopal Conference, the UN High Commissioner for Human Rights and the Inter-American Commission on Human Rights (IACHR)

IACHR chief Paulo Abrao said on Twitter that he was aware of "the violent repression of towns in Masaya."

The government, he added, seemed to be "ignoring the dialogue" with the opposition.

The semi-official website El 19 Digital said that government forces had "liberated" the town of Niquinohomo as part of a "clean-up operation" in several southern towns, including Monimbo.

Monimbo has been a center of resistance against the government of President Daniel Ortega since a wave of protests began April 18 over a since-aborted pension reform plan.

Since then, violence has claimed over 270 lives, most of them civilians, according to CENIDH.

The latest violence came a day after some 200 students, besieged by pro-government forces for 20 hours in a parish church in Managua next to the National Autonomous University of Nicaragua (UNAN), were finally allowed to leave following the intercession of Catholic bishops.

The UNAN was a last bastion of student resistance.

"They were shooting to kill," said one young man. "It was very hard."

That operation, which saw students and a few journalists huddling on the floor of the church as bullets whizzed around the building, left two people dead and 14 injured, church officials said.

The bishops' conference, which has been trying to mediate between the two sides, issued a statement late Saturday accusing the government of refusing to "dialogue sincerely and look for real processes that lead us toward a true democracy."

The bishops have called on the government, among other things, to move up scheduled elections from 2021 to 2019, but Ortega has rejected that idea.

Protesters want him and his wife, Vice President Rosario Murillo, to resign, accusing the two of corruption and despotism.