An Israeli army spokesman said on Monday evening: "A force identified armed gunmen coming toward them in a threatening way. The soldiers fired at them and identified three hits."
It is unclear if the men were killed in the shooting which is one of the most serious incidents since a ceasefire between Israel and Hezbollah began on August 13.
In Jerusalem, Terje Roed-Larsen, United Nations special envoy to Lebanon, said that he was confident the ceasefire would hold.
There is "optimism that there will be now full respect of the ceasefire and full support of the parties for its implementation," he said, speaking after meeting Tzipi Livni, the Israeli foreign minister, on Monday.
Israel remains on alert
Israel has remained ready for a resumption of hostilities and continues to hold positions inside Lebanon.
More than 250 Israeli troops, backed by about 30 armoured vehicles, were seen at nine positions within Lebanon, the AFP news agency reported on Monday.
Israel has also insisted that all airlines which have resumed flights to and from Lebanon's war-damaged capital should be routed through Jordan for security checks.
Israel fears that Hezbollah will use the truce to re-arm and import more weapons.
The Israeli air force violated Lebanese airspace four times on Monday, UN peacekeepers said, prompting protests from Fuad Siniora, the prime minister.
Siniora wrote to Kofi Annan, secretary-general of the UN, and other foreign leaders "to inform them of the dangers to security posed by these Israeli violations of Security Council Resolution 1701," Lebanese officials said.
Arabs claim victory
Middle Eastern leaders have also begun to analyse the consequences of the four-week conflict in which Israel failed to defeat Hezbollah.
Sheikh Hamad bin Khalifa Al Thani, the emir of Qatar, said that the Lebanese "resistance" amounted to the first Arab "victory" against Israel, saying it could improve prospects for peace in the Middle East.
"The Lebanese people and their resistance have achieved the first Arab victory, something we had longed for," the emir told a joint press conference in Beirut with Emile Lahoud, the Lebanese president.
Beirut's war damaged airport is returning to normal
Al Thani is the first Arab leader to visit Lebanon since the start of the war.
"Following the war ... between Lebanon and Israel, the chance to achieve peace is greater than any other period in the past," he said.
"The Israelis used to be able to dominate Arabs with military might, but this is no longer possible after what happened in southern Lebanon," he said.
In Egypt, one of two Arab states to have signed a peace treaty with Israel, Hamdeen Sabahy, head of the leftist Karama Arab nationalist party, wrote an editorial in the party's weekly mouthpiece, also called Karama entitled Getting Rid of Israel.
"The key result of [Hezbollah's] victory was to give back confidence to the Arab nation to establish its proper agenda... that is to end the existence of Israel," Sabahy wrote.
Israel ponders consequences
Meanwhile, Israel's government watchdog launched an investigation into the war as Ehud Olmert, the prime minister, rejected mounting public calls for a sweeping inquiry into the 34 day offensive.
State comptroller Micha Lindenstrauss's office announced that it would assemble "information, documents and protocols" related to the war that failed to meet Israel's stated objectives of destroyed Hezbollah and prevent it from launching rockets at Israeli cities.
"The office's different departments overseeing security, army and various government ministries will contribute their experts to examine the conduct of the war and the situation on the home front," Lindenstrauss's office said.