Israeli airstrikes killed a schoolboy and two other Palestinians in the Gaza Strip on Sunday, while Gaza rocket squads fired salvos into southern Israel, deepening the worst round of violence between the sides in more than a year. The Israeli military said its aircraft targeted rocket launchers and a Gaza health official said the 12-year-old boy, a 60-year-old farm guard and a militant were killed as the exchanges of fire entered their third day. Egyptian efforts to achieve a cease-fire faltered, spurned by the two factions in the territory responsible for the rocket fire. The violence has shattered a monthslong lull and was touched off on Friday by an Israeli air assault that killed the commander of the Popular Resistance Committees militant group, an ally of Gaza's Hamas rulers. Since then, Israeli airstrikes have killed 16 Gazan militants and two civilians, and fighters in the territory have fired more than 120 rockets at Israel, seriously wounding two civilians.