Fifteen killed in Nicaragua protests

Pro-government groups have opened fire on marchers in Nicaragua, witnesses say, killing at least 15 as more than a month of violence in the country continues.

Fifteen people have died in violence that erupted around protests on Nicaragua's Mother's Day. (AAP)

At least fifteen people have been killed and more than 200 injured in one of the worst days of violence since protests against Nicaraguan President Daniel Ortega began more than a month ago, police say.

The bloodshed on Wednesday was condemned by the Central American country's Episcopal conference of Catholic bishops, which called it "organised and systematic aggression" and suspended talks with the government that had been scheduled for Thursday.

Witnesses said pro-government armed groups opened fire on the marchers during a demonstration on Wednesday, Nicaragua's Mother's Day.

The march was held to remember the children who were among more than 80 killed since the start of protests.

"The number of people killed as a product of the actions of delinquent groups who operate wearing masks is 15," said National Police Sub-Director Francisco Diaz, saying seven of those died in the capital, Managua.

He said 218 people were injured.

The government denied allegations by rights groups that the aggressors were government supporters and said it bore no responsibility for the violence since the student-led protests started in April, triggered by proposed changes to the social security system.

Ortega was elected for a third consecutive term in 2016 with more than 70 per cent of the vote, a result questioned by observers who said the government had suppressed opposition.

In a letter to Ortega published on Wednesday, business association COSEP urged the 72-year-old president to call early elections.