Major-General Moshe Kaplinsky, the army's deputy chief of staff, said Israel had not ruled out deploying "massive ground forces" in the country.
"If we have to do this, we will. We are not ruling it out," he said.
Some Israeli troops crossed into southern Lebanon to carry out attacks on Hezbollah outposts early on Wednesday.
An Israeli army spokesman called the operations "restricted, pinpoint attacks".
Israeli soldiers have crossed into southern Lebanon several times in recent days to destroy Hezbollah posts, returning soon afterwards.
Major-General Udi Adam, the head of the Israeli army's northern command, told Army Radio on Tuesday that the fighting, which has killed at least 235 people in Lebanon and 25 in Israel, could last "a few more weeks".
Israeli warplanes struck an army base outside Beirut and other areas in south Lebanon on Tuesday, killing 17 people, and Hezbollah rockets battered towns across northern Israel, killing one person.
Diplomatic efforts to end the fighting have been continuing, with a UN mediation team meeting Israeli leaders a day after speaking with Lebanese officials in Beirut.
"The start of negotiations will not stop this operation, only the return of the kidnapped soldiers will"
Israeli prime minister
Tzipi Livni, the Israeli foreign minister, who met the delegation, said a ceasefire would be impossible unless the soldiers captured by Hezbollah in a cross-border raid last week were released and Lebanese troops were deployed along the border, with a guarantee that Hezbollah would be disarmed.
In Washington, Condoleezza Rice, the US secretary of state, said any ceasefire should be based on fundamental changes that would have a lasting impact on the region.
"We all want a cessation of violence. We all want the protection of civilians. We have to make certain that anything that we do is going to be of lasting value."
Ehud Olmert, the Israeli prime minister, said in a statement "the start of negotiations will not stop this operation, only the return of the kidnapped soldiers will."
The week-old offensive was caused by the soldiers' capture, and Olmert said Iran, a patron of Hezbollah, was behind the raid to distract the world and the G8 summit from the country's nuclear programme.
"To my regret, Iran's trick succeeded, everybody remembers the G8 decision on the subject of Lebanon and are not dealing with the Iranian issue."
Israel's offensive was initially aimed at freeing the soldiers but has broadened into a larger campaign to neutralise Hezbollah.
Israel, which has mainly limited itself to attacks from the air and sea, had been reluctant to send in ground troops because Hezbollah is far more familiar with the terrain and because of still-fresh memories of Israel's ill-fated 18-year-occupation of south Lebanon that ended in 2000.
Kaplinsky said Israel had no intention of getting bogged down in the region a second time.
Israel has been reluctant to send
in its ground troops to Lebanon
"We certainly won't reach months, and I hope it also won't be many more weeks. But we still need time to complete the operation's very clear objectives," he said.
Tony Snow, the white house spokesman, declined to react to Kaplinsky's comments, but said the administration was not happy with the current situation.
"A ceasefire that would leave the status quo ante intact is absolutely unacceptable. A ceasefire that would leave intact a terrorist infrastructure is unacceptable," he said. "So what we're trying to do is work as best we can toward a ceasefire that is going to create not only the conditions, but the institutions for peace and democracy in the region."
A proposal to send a new international force to reinforce the current 2,000-member UN force in south Lebanon gained steam on Tuesday, with Kofi Annan, the UN secretary-general, saying that a new force must be "considerably" larger and better armed than the current interim one.