On Sunday Israeli forces crossed Lebanese airspace and struck an area that Israel said was a training-camp for militants deep inside Syria as retaliation for a suicide bombing in Israel on Saturday. An assault on Monday from Lebanese territory across the Blue Line marking the Israeli line of withdrawal killed an Israeli soldier.

"Attacks and counter-attacks like these are leading us down a steep and precarious path toward more violence. I seriously advise the parties not to travel down that road. Instead, all parties should respect Security Council resolutions and the rules of international law," Mr. Roed-Larsen, UN Special Coordinator for the Middle East Peace Process, said after talks in Beirut with Lebanese President Emile Lahoud. He is on the first leg of a regional tour that will also take him to Syria and Jordan.

"Specifically, this means that the Government of Israel must refrain from the unilateral use of force, address its complaints to the Security Council and stop violations of Lebanese airspace," he said. "The Government of Lebanon must exert control over the use of force from all its territory and prevent all attacks across the Blue Line in whatever terms."

He said he was extremely worried about the new and complex web of conflicts in the region, "which has been widened and deepened by the potential reopening of a new front between Israel and Syria and a potential breaking up of the Blue Line."

These developments came against the backdrop of a political vacuum in Israeli-Palestinian relations and a wider context of "difficult situations" in Iraq and Afghanistan, Mr. Roed-Larsen said.