ADEISSEH, Lebanon (AP) - Lebanese and Israeli troops exchanged fire Tuesday in a fierce border battle that killed a senior Israeli officer, two Lebanese soldiers and a journalist - underlining how easily tensions can re-ignite along the frontier where Israel and Hezbollah fought a war four years ago.

It was the worst fighting since 2006 in the area, where Israeli and Lebanese soldiers patrol within shouting distance of each other, separated by the U.N.-drawn Blue Line boundary.

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 Hezbollah said it offered to help the Lebanese army but in the end did not get involved. "We told our brothers, control yourselves and don't do anything," Hezbollah leader Sheik Hassan Nasrallah in a televised speech.

But, he warned, his fighters would intervene if Israeli troops ever attack Lebanese forces again. "Any Israeli arm extended against the Lebanese military will be cut off by the resistance," said Nasrallah, whose arsenal is far more powerful than the Lebanese army's.

Tuesday's violence stoked fears that have been brewing for months on both sides that a new conflict could come soon.

The U.N. Security Council urged "utmost 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.