SAN JOSE (Reuters) - U.N. Secretary-General Antonio Guterres said on Monday that groups linked to Nicaragua’s government were using “unacceptable” lethal force against citizens, and urged an end to violence that has killed at least 275 people in months of protests.

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In the Nicaraguan capital, Managua, hundreds of people took to the streets demanding justice for victims of the violent crackdown on protests against President Daniel Ortega, after 12 more people were killed over the weekend.

“It’s evident that there is a shocking number of deaths and a lethal use of force by entities tied to the state that is unacceptable,” Guterres told a news conference in neighboring Costa Rica.

“It’s essential to immediately halt the violence and rebuild national political dialogue. Only a political solution is acceptable,” Guterres added, speaking at the 40th anniversary of the Inter-American Court of Human Rights.

At least 275 people have died since unrest broke out in April, according to the Nicaraguan rights group CENIDH, when Ortega attempted to trim pension benefits. The government later dropped the plan, but its heavy-handed response to the demonstrations sparked a wider protest against Ortega’s rule.

The attacks have drawn international condemnation of Ortega, a former Marxist guerrilla leader facing his biggest test in office since he returned to power in 2007.

Ortega says he is open to dialogue, and has invited the Inter-American Commission on Human Rights to verify his assertion that human rights have been respected in the country.

Violence surged again over the weekend when armed groups and police loyal to Ortega burst into universities occupied by protesters and smashed roadblocks set up in defiance of the government.

In a statement on Monday, the U.S. State Department called on Ortega’s government to heed Nicaraguans’ call for democratic reforms immediately and hold elections.

The United States has imposed visa restrictions on individuals it holds responsible for human rights abuses or undermining democracy in Nicaragua, as well as their family members.

Relatives of victims of the violence walked down the main streets of Managua on Monday with their coffins, demanding justice for the dead.

“The population hasn’t given up because it’s still in the streets demanding freedom,” said Carlos Tünnermann, a member of the Civic Alliance for Justice and Democracy, one of the main civilian groups leading the opposition to Ortega.

The opposition has called on Ortega to step down and hold early elections.