Leftist rebels bombed 10 Lima electric towers and set off scores of bombs near the U.S. Embassy and other capital targets in an overnight onslaught that President Fernando Belaunde said yesterday was an "undeclared war."

Parts of the capital were blacked out for 90 minutes but there were no reports of casualties, United Press International said. Police said they arrested 20 suspected rebels soon after the dynamiting began.

During the blackout, the guerrillas set off dynamite and incendiary bombs near the U.S. Embassy, the presidential palace, the Sheraton Hotel, several banks and the Bayer Chemical industrial complex.

"What happened last night are clear acts of treason and sabotage against the nation," Belaunde said in a brief news conference. "We must all unite against these criminal mercenaries, in their undeclared war against Peru." He was referring to Sendero Luminoso (Shining Path) guerrillas, a self-styled Maoist group held responsible for more than 1,000 terrorist attacks.

Damage in most of the bombings was minor. But at the Bayer plant, a third of which is owned by the government, explosions sparked a huge fire. Damage at the plant, one of the largest chemical industrial complexes in South America, was estimated at $300 million.