Israeli and Lebanese troops fought a rare cross-border skirmish on Tuesday that killed four Lebanese and an Israeli officer in the most serious violence along the frontier since a 2006 war.

The Iranian- and Syrian-backed Hezbollah group, which battled Israel in the war four years ago, took no part in the exchange of fire. There was no sign of any extensive Israeli preparations for a large-scale operation -- an early indication the clash might not trigger a wider conflict.

"It started when the Israelis wanted to cut a tree down inside Lebanon. The Lebanese army fired warning shots at them and they responded by shelling," said a security source in Lebanon.

Israel's shekel currency fell against the dollar because of concern about the incident. "If the military says it's going to be a big thing, the dollar will go up tomorrow," said a dealer at Israel Discount Bank.

United Nations peacekeepers appealed to both sides to exercise "maximum restraint" after the incident.

A new Lebanon war could be even more devastating than the last. Hezbollah has an arsenal of 40,000 rockets, according to Israeli estimates. Israel has threatened to attack Lebanese infrastructure in any new conflict with the Shi'ite guerrillas.

Lebanese Prime Minister Saad al-Hariri "denounced the Israeli violations of Lebanese sovereignty". His office said he also contacted Egyptian President Hosni Mubarak to discuss "ways to confront the Israeli aggression against the Lebanese army".

Israel's Foreign Ministry said it would file a complaint at the United Nations over the clash, accusing Beirut of violating the 2006 Security Council resolution that ended the war.

"Israel views the Lebanese government as responsible for this serious incident and is warning of the ramifications if the violations continue," the ministry said in a statement.

The Israeli military said its troops were fired upon while engaged in "routine activity" inside Israeli territory, between an Israeli security fence and a U.N.-drawn border line.

An Israeli helicopter fired two missiles at a Lebanese army post near Adaisseh village, destroying an armoured personnel carrier. A security source said three Lebanese soldiers and a Lebanese journalist were killed and five people wounded.

Witnesses said Israeli artillery also fired at the village.

Hezbollah's Al Manar television said a high-ranking Israeli soldier was killed on the border. The Israeli military had no immediate comment.

The fatalities were the first suffered by either side since the 2006 war in which 1,200 people, mostly civilians, were killed in Lebanon, along with 158 Israelis, mostly soldiers.

That conflict began after Hezbollah attacked an Israeli border patrol, killing eight soldiers and abducting two others, whose bodies were later returned in a prisoner swap.

A 13,000-strong U.N. peacekeeping force known as UNIFIL patrols southern Lebanon under a U.N. resolution that expanded its mandate and ended the war on Aug. 14, 2006. UNIFIL said it was examining the circumstances of the bloodshed.

The incident occurred a day after rockets that Israel suspects were fired from Egypt by Islamist militants struck Jordan's Red Sea port of Aqaba, killing a man.

"(There is) a necessity to repel any Israeli attempt of aggression no matter what the circumstances," Lebanese President Michel Suleiman was quoted as saying. He urged the use of diplomacy to deal with the border incident.