A Nicaraguan air force helicopter crashed about 125 miles north of Managua, killing all 15 Sandinista soldiers and crewmen aboard. The government said that initial reports indicated the crash was an accident. But guerrillas said in a radio broadcast that their forces used a surface-to-air missile to shoot down the MI-17 helicopter. The U.S.-supported contras claim to have shot down six of the Soviet-made helicopters since their war with the Sandinistas began in 1981. The Nicaraguan government has acknowledged losing only two of the craft.