MANAGUA, Nicaragua -- More than a dozen people died in shootings that erupted around Mothers' Day protests in Nicaragua, but the government and human rights groups differed Thursday on who was to blame.

The Nicaraguan Center for Human Rights, which said it had members participating in Wednesday's march, said at least 11 people died when peaceful marches were attacked "by the repressive police and shock forces" loyal to President Daniel Ortega, the latter a reference to pro-government youth groups.

Francisco Diaz, the second in command of the national police, said there were 15 deaths nationwide, which he blamed on "criminal gangs." Foreign Minister Denis Moncada said the violence was generated by opposition political groups and said, "The government rejects any responsibility in that violence."

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The Mother's Day marches were led by mothers of the victims of earlier protests. But some ended with gunmen firing into crowds sending thousands of demonstrators running for cover.

Anti-government protesters take part in a march in support of "the Mothers of April" movement - whose children died in the protests - on Nicaragua's National Mothers Day, in Managua on May 30, 2018. Diana Ulloa/AFP/Getty Images

An Associated Press photographer at Wednesday's march in Managua saw one person with a wound to the head carried off in a stretcher with a sheet covering his upper body, apparently dead.

The gunfire appeared to come from government supporters near the end of the march, but demonstrators armed with improvised bottle-rocket launchers also opened fire in the skirmish.

The country's Roman Catholic church hierarchy said in a statement Thursday that the violence showed that it couldn't yet resume a dialogue between protesters and President Daniel Ortega's government.

Amnesty International, which also had a delegation accompanying the Managua march, said in a statement that Wednesday's violence showed a "systematic shoot-to-kill policy" on the part of the government. It blamed police and Sandinista gangs.

Shortly before the attacks Wednesday, Ortega told supporters at a rally that he was committed to peace.

Protests began in mid-April in response to changes to the social security system, but expanded to call for Ortega's exit.

"It appears that Ortega is prepared to stay in power no matter the cost, no matter the number of people who have to die," said political analyst Oscar Rene Vargas.