Beirut, Lebanon ? More Israeli troops surged into southern Lebanon on Saturday, reaching the Litani River and engaging in some of the heaviest combat of the monthlong war just hours after the U.N. Security Council adopted a cease-fire plan. Israel lost 19 soldiers – its highest one-day toll.

The leader of the Islamic militant group Hezbollah grudgingly joined Lebanon’s government in accepting the U.N. resolution but vowed to keep fighting until Israeli troops leave and hand over territory to a muscular U.N. peacekeeping force intended to separate the antagonists.

Israel also signaled its intention to approve the plan at a Cabinet meeting today, and a senior official predicted fighting would stop Monday morning, but there was no slowing in the bloodshed.

U.N. Secretary-General Kofi Annan announced that a cease-fire would take effect at 8 a.m. Beirut time Monday (midnight CDT), saying both Israeli and Lebanese leaders agreed to the start time. In his statement issued in New York, Annan called for an immediate halt to the fighting.

Israel was determined to batter Hezbollah until the end, while the guerrillas seemed to be fighting as fiercely as ever after a month of intense Israeli air, artillery and ground assaults.

Israel’s military said 19 soldiers were killed, five more were missing and more than 70 were wounded after the first day of the expanded offensive. The broadened push tripled troop strength to 30,000 in southern Lebanon. Israel Radio reported 100 troops wounded, which if confirmed would be the Jewish state’s highest one-day injury toll of the fighting.

Smoke billows Saturday from a destroyed clothing factory after an Israeli air strike early Friday in the Hezbollah stronghold suburbs of Beirut, Lebanon.

Israel confirmed that guerrillas shot down a military transport helicopter in the south and the five people aboard, all crew members, were missing. Hezbollah said a battle raged for hours as Israel attempted to reach the crew, but there were no details of that fighting. Hezbollah claimed to destroy 21 tanks.

Israel said it killed more than 40 Hezbollah fighters. Hezbollah issued a statement saying three of its fighters had been killed but gave no date.

Nineteen Lebanese civilians died from Israeli airstrikes, while Hezbollah rockets wounded eight people in northern Israel. The 32-day struggle has claimed nearly 900 lives.

The big expansion of Israel troop strength prompted Hezbollah’s leader, Sheik Hassan Nasrallah, to declare the fight far from finished and likely to get worse.

“We must not make a mistake, not in the resistance, the government or the people, and believe that the war has ended. The war has not ended,” he said.

“Today nothing has changed and it appears tomorrow nothing will change,” Nasrallah added in his trademark measured tones.

Speaking a few hours before Lebanon’s Cabinet voted unanimously to accept the U.N. plan, Nasrallah said Hezbollah would abide by the cease-fire resolution but continue fighting as long as Israeli troops remained in Lebanon, calling it “our natural right.”

Lebanese Prime Minister Fuad Saniora said his Cabinet endorsed the cease-fire plan despite having reservations. “We will deal with the requirements of the resolution with realism in a way that serves the national interest,” he said.

The Cabinet harshly condemned Israel’s military push Saturday, saying it presented a “flagrant challenge” to the international community after the U.N. resolution was issued.

A senior Israeli official, who spoke on condition of anonymity because he was not authorized to discuss sensitive issues publicly, said Israel wanted to seize control of the south so more Hezbollah fighters do not enter the zone before it is handed over to the Lebanese army and U.N. troops.

Defense Minister Amir Peretz said Israeli troops would remain until the international force arrived, and would defend themselves if attacked.