Four people are dead after troops from Israel and Lebanon exchanged gunfire along the border Tuesday, the most serious fighting since a fierce war along the frontier ended four years ago.

Israeli soldiers use a crane seemingly to cut a tree near the border with Lebanon, near the southern village of Aadassi. Israel and Lebanon each claimed the tree was in its territory. (Lutfallah Daher/Associated Press)

Accounts of what sparked the clash differed.

Israeli military spokesman Capt. Barak Raz said the fighting broke out as soldiers were on a routine patrol. He said the soldiers were inside Israeli territory when they came under fire and they retaliated with artillery fire.

A spokesman for the Lebanese army said the clash occurred as Israeli troops tried to remove a tree from the Lebanese side of the border. An Associated Press photo appears to show an Israeli standing on a crane reaching over the fence to get at a tree.

"It was over the fence but still within Israeli territory," the office of the Israeli military spokesman said.

An Israeli shell hit a house in the Lebanese border town of Aadassi, the Lebanese spokesman said.

Israeli military officials said a 45-year-old battalion commander with the rank of lieutenant colonel was killed in the gunfire, while an officer for the Lebanese army said at least two of its soldiers and a journalist working for the daily Al-Akhbar newspaper, Assaf Abu Rahhal, were killed.

The officials all spoke on condition of anonymity under military guidelines.

The Israeli-Lebanese border has been relatively quiet since the summer 2006 Israel-Hezbollah war that left 1,200 Lebanese and about 160 Israelis dead. Tuesday's fighting did not appear to involve Hezbollah fighters.

After the 2006 war, the United Nations deployed a 12,000-member peacekeeping force, known as UNIFIL, in the area. The agency confirmed the incident Tuesday. Although it declined to offer details, UNIFIL issued a statement urging "maximum restraint" on both sides.

"UNIFIL peacekeepers are in the area and are trying to ascertain the circumstances of the incident and any possible casualties," said spokesman Neeraj Singh. "Our immediate priority at this time is to restore calm in the area."

Lebanese President Michel Suleiman denounced the fighting and urged the army commander to "confront any Israeli aggression whatever the sacrifices."

With files from The Associated Press