The fighting flared into Israeli tank, helicopter and artillery strikes near this Lebanese town, but ended after several hours and there was no sign that either side was preparing to escalate. The Shiite guerrilla force of Hezbollah, which says its massive arsenal is intended to defend Lebanon from Israel, did not get involved.
But Hezbollah's leader Sheik Hassan Nasrallah warned in a televised speech that his fighters would intervene if Israeli troops ever attack Lebanese forces again. Though Tuesday's incident was finished, he said, "any Israeli arm extended against the Lebanese military will be cut off by the resistance."
The violence stoked fears that have been brewing for months on both sides that a new conflict could come soon.
The U.N. urged "maximum restraint." U.S. State Department spokesman P.J. Crowley said, "The last thing that we want to see is this incident expand into something more significant." Both the U.S. and the U.N. said they were working to determine the exact circumstances of the fight.
Tuesday's clashes began after an Israeli soldier tried to remove a tree along the border, something the military has done in the past to improve its sightlines into Lebanon.
But both sides claimed the tree was in their territory. An Associated Press photo shows an Israeli standing on a crane reaching over the fence that Israel erected to separate the two countries. The fence, however, does not match the Blue Line in all places, and the Israeli military said in a statement that the tree was in Israeli territory.
"It was over the fence but still within Israeli territory," the military spokesman's office said. He said the tree cutting was coordinated with the U.N. peacekeeping force in south Lebanon, UNIFIL.
The Lebanese military said the Israelis crossed onto Lebanese soil despite calls from the U.N. and Lebanon to stop. When the Israelis persisted, Lebanese troops opened fire with small arms and rocket-propelled grenades, it said in a statement.
The Israeli forces responded with "machine guns and tank shells, targeting Lebanese army positions and civilian homes in the area," the Lebanese military said. It said two soldiers were killed and a third seriously wounded.
Ronith Daher, 32, a Lebanese journalist who was at the scene, said she saw a UNIFIL peacekeeper ask Israel not to allow the Israeli soldier to cross the fence and warned them the Lebanese troops would open fire.
Israel, however, accused Lebanon of provoking the fight. The Israeli military's northern commander, Maj. Gen. Gadi Eizenkot, said that while soldiers were removing bushes by the fence, Lebanese military snipers shot two officers who were more than 300 meters (yards) away.
A lieutenant colonel was killed and a captain was critically wounded, the Israeli military said.
Israel responded with infantry, tanks and artillery fire and later hit a Lebanese army base and command center with helicopter and artillery fire, Eizenkot said.
"These are the first casualties in the past four years (in the border area). We view this very seriously and that is why we responded so severely," he told reporters.
Israeli Defense Minister Ehud Barak also demanded that Lebanon and UNIFIL investigate the "murderous attack." Prime Minister Benjamin Netanyahu vowed that Israel will "will respond to any disturbance of the peace on the border and (attempts) to harm civilians and the soldiers protecting them."
In Adeisseh, a border village home to several thousand people, rubble was strewn in the streets, the door of a shop was blown out, and the balcony of a home had been hit with a shell.
A Lebanese journalist with the daily Al-Akhbar newspaper, Assaf Abu Rahhal, was killed when an Israeli shell landed next to him in Adeisseh, a security official said, speaking on condition of anonymity under military guidelines. Three civilians were wounded, including Adeisseh's mayor, said Ali Rahal, 44, a local businessman.
Lebanese President Michel Suleiman urged the military to "confront any Israeli aggression whatever the sacrifices."
The border has been relatively quiet since the summer 2006 Israel-Hezbollah war that left 1,200 Lebanese and about 160 Israelis dead. After the war, the U.N. beefed up its peackeeping force to 12,000 members and the Lebanese military deployed in the border region for the first time in years.
The Lebanese military's tough response to the Israeli border move may have aimed to show that it is capable of defending Lebanon - a role that Hezbollah often touts for itself.
Hisham Jaber, who heads the Middle East Center for Studies and Public Relations in Beirut, said Israel might have provoked the clashes to try to get Hezbollah to show its hand. "Israel wanted to lure Hezbollah into joining the fight ... to entice Hezbollah to come up to the surface," he said.
Tensions along the border have risen in recent months. Israel claims Hezbollah has significantly expanded and improved its arsenal of rockets since 2006, with help from its allies Syria and Iran. Adding to the friction, more than 70 people in Lebanon have been arrested since last year on suspicion of collaborating with Israel.
--- Associated Press Writers Elizabeth A. Kennedy in Beirut, Ian Deitch in Jerusalem and Matthew Lee in Washington contributed to this report.