KIRYAT SHMONA, Israel (Reuters) - Israel told tens of thousands of northern residents on Monday to remain in underground bomb shelters while its war planes raided Hizbollah targets in Lebanon to avenge the killing of four Israelis. The United States said it was concerned about the tensions after Israel vowed to strike at Hizbollah guerrillas "on the ground, from the air and the sea" in response to a bombing on Sunday that killed an Israeli general, two soldiers and a journalist in Israel‘s south Lebanon occupation zone. But no unusual military activity was apparent beyond the air raids. The army said planes struck "infrastructure targets" of the Iranian backed guerrilla group and bombed weapons depots. Northern residents were bracing for rocket attacks by Hizbollah in response to the raids. The air attacks and threatened offensive were the sharpest escalation in Israel‘s simmering Lebanon conflict since a 1996 Israeli assault in which more than 200 Lebanese – most of them civilians – were killed and thousands driven from their homes. Israeli Prime Minister Benjamin Netanyahu convened his security cabinet at 10 a.m. to discuss the situation in Lebanon. Israel announced the offensive hours after a roadside bomb went off near an Israeli convoy in its south Lebanon occupation zone on Sunday killing Brigadier-General Erez Gerstein. Gerstein headed the army‘s liaison unit with the United Nations and was the highest ranking officer to die in Lebanon combat since the first days of Israel‘s 1982 invasion of its northern neighbour. Zeev Schiff, one of Israel‘s most prominent military analysts, said on Monday that the roadside bomb attack was the pretext for an Israeli offensive planned weeks ago. Hizbollah, which is fighting a guerrilla war to oust Israel from the zone, celebrated its attack into the night and vowed to continue fighting until Israel withdrew its troops The deaths raised to seven the number of Israelis killed in south Lebanon since the start of the year – all of them in two incidents in the past week – compared with the 21 who died in action during all of 1998. Israel has occupied parts of south Lebanon since 1978 and set up the so-called security zone in 1985 with the declared aim of preventing guerrilla attacks on its northern border.