President Daniel Ortega on Monday slammed as a "massacre" an attack on his political supporters that killed five people and left 28 more hurt.
"This was a genuine massacre, one that has been condemned by the nation," the leftist president said at a memorial for the dead at a convention center, carried on state and pro-government media.
Unidentified assailants opened fire late Saturday, in Matagalpa department, on buses bringing supporters back from a party in Managua to celebrate the 35th anniversary of the 1979 revolution.
The civilian Sandinista party supporters "were ambushed on a highway with rifles (by men) who fired on buses bringing some of the families that had come (to the capital area) for the event," Ortega added.
"These are expressions of rancor, of hatred. ... They are a minority, but they are there, latent and suddenly crop up in abominable deeds like these," the president said.
On Saturday, thousands of supporters gathered at the Plaza La Fe, north of Managua, to celebrate the Sandinista rebel victory in 1979 over the dictatorship of Anastasio Somoza, whose family had run Nicaragua like their own estate since 1936.
The most prominent guest was Venezuelan President Nicolas Maduro, whose oil-rich nation provides millions of dollars in aid to impoverished Nicaragua.
Ortega, now 68, was one of the rebel Sandinista leaders that toppled Somoza. He was Nicaragua's leader from 1979-1990, and returned to power in 2007.