Two soldiers and two civilians were reported wounded in a reb-el attack on air force headquarters with truck bombs and explosives lobbed by catapults.

Also Tuesday, a fourth mayor in San Miguel province resigned after receiving death threats from the leftist rebels, who accused the officials of participating in a U.S.-backed counter-insurgency plan.The attack on Ilopango air base was the first in nearly seven years and the second this month on a major military installation in the capital. Witnesses said it began in late morning with nearly simultaneous explosions of two pickup trucks.