The Lebanese authorities have been asked to stop the clashes

There are also reports of Katyusha rockets being fired at northern Israel early on Wednesday.

In retaliation, Israeli warplanes raided suspected guerrilla positions.

Mr Annan, the EU, Russia and the US - meeting in Madrid - condemned the attacks on Israel from across the border.

The UN secretary general called on the Lebanese Government and "all relevant parties" to prevent them.

He did not mention Syria, a major power broker in Lebanon - but correspondents say his intention was clear.

Hezbollah claims success

Hezbollah has been launching almost daily attacks on the Shebaa region since Israeli forces began their offensive in the West Bank 12 days ago.

The latest clashes erupted after guerrillas fired on three Israeli army positions in the Shebaa area - near the border between Israel, Lebanon and the Israeli-occupied Goland Heights captured from Syria in 1967.

The guerrillas are said to have attempted to take over an Israeli outpost on Rweisat al-Alam hill. They claim to have destroyed an Israeli tanks and equipment as well as causing casualties, but there has been no confirmation.

Several rockets fired by Hezbollah directly hit an Israeli radar post on Mount Hermon, in the foothills of the Golan Heights, witnesses and security sources said, and smoke was seen rising over the Israeli positions.

Disputed territory

Israel responded with artillery fire and air strikes, expanding its attacks for the first time to hit targets in the Bekaa valley

Earlier, military sources in northern Israel said rockets and mortars fired from the Lebanese side of the border fell near the town of Kiryat Shmona, but no casualties were reported.

On Monday, the Israeli army called up fresh reservists for possible deployment on the northern border.

Along with the Lebanese and Syrian authorities, Hezbollah claims the area is part of Lebanon from which Israel should have withdrawn when its forces ended their occupation in May 2000.

But Israel says the farms are on the Syrian side of the border and so are part of the Golan Heights, which it has occupied since 1967.