Hizbollah fighters shot down an Israeli helicopter in southern Lebanon, Hizbollah television and a Lebanese security source said.
Hizbollah leader Sayyed Hassan Nasrallah said his fighters would abide by Friday's UN Security Council resolution calling for a "full cessation of hostilities" once the timing of the truce was agreed and once Israeli forces also adhered to it.
Earlier, the UN Security Council unanimously adopted a resolution on Friday calling for an end to the month-old war between Israel and Hizbollah.
The resolution, negotiated by the United States and France, authorised up to 15,000 UN troops to be deployed to monitor a withdrawal of Israeli troops from southern Lebanon and to help the Lebanese army enforce a cease-fire. Israeli Prime Minister Ehud Olmert told US President George W Bush he backed the resolution, an Israeli government official said.
"The Prime Minister spoke with President Bush and thanked him for his assistance in keeping Israeli interests in mind at the Security Council," the official said. The UN resolution called for a "full cessation of hostilities". Hizbollah should stop all attacks immediately and Israel should end "all offensive operations", it said.
Israel would halt offensive operations in Lebanon at 0400 GMT on Monday but would continue to engage Hizbollah in areas where the army was operating, a senior government official said. Foreign Minister Tzipi Livni also said the offensive would end on Monday but did not specify a time.
Helicopters lifted hundreds of Israeli troops into south Lebanon as part of an expanding offensive launched even though Prime Minister Ehud Olmert has backed the UN vote. Olmert was expected to ask his cabinet to approve the resolution on Sunday.
Lebanon's government unanimously approved the resolution in a session on Saturday, Lebanon's prime minister said.
Lieutenant-General Dan Halutz, Israel's top general said Israel had tripled its forces in Lebanon since Thursday.
Arab television stations said 17 Israeli soldiers were killed on Saturday, which would be the highest single-day death toll of the war for the Israeli military.
Israeli television earlier reported seven soldiers killed-five in fighting and two crushed beneath an Israeli tank.
The Israeli army said more than 50 soldiers had been wounded. It said it had killed more than 40 Hizbollah fighters in the last 24 hours and destroyed several rocket launchers. Hizbollah denied it had lost 40 fighters in the clashes.
Israeli air strikes killed up to 20 people on Saturday, Lebanese security sources said. Hizbollah fired at least 65 rockets into Israel-a considerable decrease from recent days-lightly wounding several people.
"Once there is an agreement to stop the hostilities or the military operations, the resistance will abide by it," Nasrallah said in a speech broadcast on Hizbollah's al-Manar television.
But he added: "As long as there is Israeli military movement, Israeli field aggression and Israeli soldiers occupying our land ... it is our natural right to confront them, fight them and defend our land, our homes, and ourselves."
He said Hizbollah would cooperate with Lebanese and UN troops due to be deployed in south Lebanon under the Security Council resolution adopted on Friday to end the month-old war.
US Secretary of State Condoleezza Rice she hoped fighting would end within "a day or so" of a cease-fire being agreed. "(UN) Secretary General (Kofi) Annan is working with the parties to establish a timetable for a cease-fire, but I would hope that within no more than a day or so of that there would be a cessation of hostilities on the ground," she said.
BUSH WELCOMES RESOLUTION US President George W Bush welcomed the resolution, saying Hizbollah and its sponsors Iran and Syria had brought an "unwanted" war to the region. Bush said the UN resolution aimed to "put an end to Iran and Syria's efforts to hold the Lebanese people hostage to their own extremist agenda".
A UN envoy said earlier the United Nations expected the Israeli assault to wind down in one to two days and an expanded international force to begin deploying in a week to 10 days.
"We are not starting from zero," Alvaro de Soto, the UN special envoy for the Middle East peace process, said, adding that several countries had offered contingents for the force.
The UN resolution authorises up to 15,000 UN troops to move into Lebanon to enforce a cease-fire. France is widely expected to lead the force, which will expand the existing UN Interim Force in Lebanon (UNIFIL), but have a stronger mandate.
French Foreign Minister Philippe Douste-Blazy made clear in an interview with Le Monde newspaper that the mission of the larger UNIFIL would not include disarming Hizbollah by force.
"We never thought a purely military solution could resolve the problem of Hizbollah," he said. "We are agreed on the goal, the disarmament, but for us the means are purely political."
UNIFIL said a Ghanaian peacekeeper had been wounded by Israeli artillery fire near the southern village of Haris. Relief officials said Israel was still denying permission for aid convoys to reach distressed civilians in south Lebanon.
Air strikes in the south killed up to 15 people in the village of Rshaf and four civilians in Kharayeb, security sources said. Raids in the Bekaa Valley killed one civilian.
Major General Udi Adam, head of the Israeli northern command, said some Israeli forces had reached as far as the Litani river in Lebanon. He said at least 500 Hizbollah fighters had been killed so far in the conflict. Hizbollah has announced fewer than 100 deaths.
At least 1,061 people in Lebanon and 131 Israelis have been killed in the war that began after Hizbollah captured two Israeli soldiers in a cross-border raid on July 12.