ADAISSEH, Lebanon, (Reuters) – Israeli and Lebanese  troops clashed on the two countries’ border yesterday, raising  concerns that a new round of fighting might erupt.

A senior Israeli officer, two Lebanese soldiers and a  Lebanese journalist were killed in the exchange of fire, the  most serious violence along the frontier since a 2006 war.

The United Nations and the United States urged both sides to  show restraint.

Hezbollah fighters, who battled Israel four years ago, took  no part in the exchange of fire.

But Hezbollah leader Sayyed  Hassan Nasrallah said the group would not stand silent if Israel  attacked the Lebanese army in the future.

Lebanon and Israel gave different accounts of the events  leading up to the clash and the U.N. peacekeeping force in  southern Lebanon said it had yet to ascertain the circumstances  leading to the bloodshed.

The Lebanese army said an Israeli patrol had crossed the  technical line of the border although U.N. peacekeepers had told  it to stop.

“A Lebanese army force then repelled it using rocket  propelled grenades. A clash happened in which the enemy forces  used machine guns and tank fire targeting army posts and  civilian houses,” it said.

Major-General Gadi Eisenkot, head of Israel’s northern  command, said Lebanese snipers fired at officers inside Israeli  territory. The Israeli army showed reporters blood stains  outside a bunker some 100 metres inside its side of the border  fence where it said the colonel was shot in the head and another  officer was shot in the chest and seriously wounded.

“There were only two or three shots,” said an Israeli  military spokeswoman. “They were standing there, where the blood  is.” They were watching other troops move a cherry-picker crane  next to a fence behind the demarcation line to trim a tree,  whose branches were tripping the fence’s electronic  anti-infiltration devices, the spokeswoman said.