Israeli officials said on Sunday that the militant Islamic group Hezbollah, striking from Lebanon, had fired shells into Israel, killing at least one person and wounding four others.
The attack on the town of Shlomi, in the western Galilee region, raised the prospect of a strong Israeli retaliation against the Hezbollah in Lebanon.
The killing of an Israeli civilian was the first by the Hezbollah, since Israeli troops withdrew from southern Lebanon three years ago.
Israel's deputy defense minister, Zeev Boim, said his government had no desire to open a new front of conflict in the region, but it could not stand by, while its citizens in the north of the country are being hurt.
Hezbollah issued a statement defending its actions, saying it had fired anti-aircraft shells at Israeli planes that had flown over southern Lebanon.
But Mr. Boim rejected this as a justification. He said the Hezbollah had not shelled Israeli aircraft, but Israeli citizens, and he accused the organization of playing with fire.
The shelling marked the fourth reported cross-border attack by Hezbollah since Friday, and the first to have caused fatalities.
Israel's foreign minister, Silvan Shalom, also reacted angrily to the latest shelling.
He warned that Israelis would be forced to defend themselves, if Syria, which is regarded as the main power broker in Lebanon, and the Lebanese government fail to prevent the Hezbollah from launching any more attacks.
Israel has also lodged a protest at the United Nations, saying it is absurd that Syria, a country that supports the Hezbollah, should be currently serving as head of the U.N. Security Council.
Israel's ambassador to the United Nations, Dan Gillerman, warned the world body that the actions of the Hezbollah guerrilla fighters in southern Lebanon are raising tensions in the Middle East and undermining efforts to reach a comprehensive peace in the region.