BEIRUT, Lebanon -- Israel intensified its air assault on Lebanon on Saturday, striking Hezbollah strongholds, bombing central Beirut for the first time, and pounding seaports and a key bridge as it tightened a noose around this reeling nation.

Trying to defuse the crisis, Lebanon's prime minister indicated he might send his army to take control of southern Lebanon from Hezbollah -- a move that might risk civil war. In a more ominous sign that the struggle could spread, Israel accused Iran of helping fire a missile that damaged an Israeli warship, a charge denied by Iran.

Hezbollah guerrillas, meanwhile, fired waves of rockets ever deeper into Israel, and Israeli officials warned that Tel Aviv, 70 miles inside Israel, could be hit.

The death toll in the four-day-old conflict rose above 100 in Lebanon, and stood at 15 in Israel.

Despite worldwide alarm, there was little indication either Western or Arab nations could muster a quick diplomatic solution. The United States and France prepared to evacuate their citizens, and Britain dispatched an aircraft carrier to the eastern Mediterranean in apparent preparation for evacuations.

Choking back tears, Saniora went on television to plead with the United Nations to broker a cease-fire for his "disaster-stricken nation."

The Western-backed prime minister, criticizing both Israel and Hezbollah, also pledged to reassert government authority over all Lebanese territory, suggesting his government might deploy the Lebanese army in the south, which Hezbollah effectively controls.

That would meet a repeated U.N. and U.S. demand. But any effort by Saniora's Sunni Muslim-led government to use force against the Shiite Muslim Hezbollah guerrillas could trigger another bloody civil war in Lebanon. Many fear the 70,000-strong army itself might break up along sectarian lines, as it did during the 1975-90 civil war.

Reacting to Saniora's statements, Israel's Vice Premier Shimon Peres said Lebanon must prove it was serious by deploying troops on the border.