BEIRUT, Lebanon -- Sudden tension flared at the border between Lebanon and Israel after Israeli planes reportedly fired two rockets that fell in the sea off the Lebanese coast.

The unexpected incident, which occurred late Tuesday night, raised concern among Lebanese political circles as it came after a long lull in violence in the volatile area patrolled by U.N. forces known as UNIFIL.

U.N. sources and witnesses said the rocket explosions coincided with the flight of Israeli helicopters over south Lebanon and UNIFIL headquarters in Naqoura, a few miles from the border.

A spokesman for the Shiite militant Hezbollah said a helicopter fired two rockets that exploded in the sea. But UNIFIL and Lebanese army sources could not confirm if the rockets originated from the air or the sea.

Prime Minister Fouad Siniora denounced the incident Wednesday and summoned the ambassadors of the five permanent members of the Security Council to complain about Israel's provocative activity and asked that their countries press Israel to stop its violations of Lebanese sovereignty.

"We refuse and condemn any act that undermines the sovereignty and independence of Lebanon," Siniora said, adding that he contacted the special representative of the U.N. secretary general in south Lebanon, Geir Pedersen, to lodge a strongly worded complaint.

Political observers raised questions about Israel's unprovoked move, which comes at a time when Hezbollah appears to be keeping a low profile.

Hezbollah has been avoiding any provocative act for the past months, especially after the passage of resolution 1558 that provides for disarming the group as well as armed Palestinian factions.

The issue of Hezbollah's arms has split Lebanon between supporters of the group's right to keep weapons and those who oppose the existence of private armies.

But there is a general consensus among various Lebanese groups and factions that the issue of Hezbollah's arms should be settled through internal dialogue. (UPI)