Guerrillas knocked out 40 percent of the nation's electric power lines and attacked military positions in at least six towns Wednesday, one day after offering to stop fighting if elections are delayed.

The Farabundo Marti guerrilla radio said four soldiers were killed and 21 injured in the attacks. Military sources who requested anonymity said that at least one guerrilla was killed and two were wounded.On Tuesday the rebels attacked two military installations, killing eight people and wounding 17. On the same day, their leaders offered to disarm if the military is sharply cut and presidential elections are postponed.

Guerrilla sabotage Wednesday put seven of the state power company's 19 high power electric lines out of service, said a spokesman for the company.

Local civil authorities said the sites attacked included the northeastern town of Metapan, the northern towns of San Miguel de Mercedes and Potonico, and the eastern towns of Usulutan and Chinameca.

In downtown San Salvador, a bomb partially destroyed a local headquarters of the National Workers' Federation, but there were no casualties and responsibility for the blast was unclear.

El Salvador's major political parties were meeting in Mexico on Tuesday with senior rebel commanders to discuss the guerrillas' proposal to end the nine-year war.

On Tuesday, rebels attacked the 4,000-member 1st Brigade's headquarters. It was the fifth attack on a major military installation in this capital since November.