Clashes broke out after the Israeli army cut down a tree on the border. Reuters

The tree that sparked a deadly confrontation between Israeli and Lebanese troops along the tense border between the two countries was on Israeli territory, the UN has said.

Five people died in the most serious clash between the two countries since the war of 2006.

Unifil, the UN force that has monitored the border since the ceasefire that ended that conflict, said that investigations had established that the tree, which Israeli troops were cutting down when Lebanese forces fired on them, was south of the "blue line" which marks the border.

"Following the exchange of fire between the Lebanese army and the Israeli army across the blue line in El Adeisse, the Unifil investigators were on the ground and commenced investigations," it said. "The investigations are still ongoing and the findings will be intimated on [their] conclusion.

"Unifil established, however, that the trees being cut by the Israeli army are located south of the blue line on the Israeli side."

Unifil confirmed that Israel had notified it of its intention to carry out routine maintenance work on trees along the border, and that Unifil passed the information on to the Lebanese army.

The Lebanese army admitted that its soldiers opened fire on troops from the Israeli Defence Forces (IDF) in the confrontation.

In a statement issued to the news agency AFP, a spokesman said: "The Lebanese army opened fire first at Israeli soldiers who entered Lebanese territory... This constituted defence of our sovereignty and is an absolute right."

An Israeli battalion commander was shot dead and another officer seriously wounded. In Israeli shelling that followed, three Lebanese soldiers and a Lebanese journalist were killed.

The IDF claimed that its forces were the subject of a planned ambush, citing the presence of Lebanese media close to the border. "We have reason to believe this was planned in advance," an IDF spokeswoman, Avital Leibovich, said. She added that the initiative could have come from Lebanese army units under the influence of the Islamist militant organisation Hezbollah.

Most analysts agreed that the incident was likely to be contained rather than flaring into an ongoing conflict along the tense border.

The dead Israeli soldier, Lieutenant Colonel Dov Harari, a 45-year-old father of four, was to be buried in the coastal city of Netanya later today.

Meanwhile, a Palestinian militant was killed in an air strike in Gaza early today. Sharif Abdel Hadi Abbey, 22, died and two others were injured in the strike close to Khan Younis, according to Palestinian souces. The IDF said aircraft had fired at Palestinians approaching the Gaza border fence.