Israel ignored urgent international appeals for restraint today and bombed two Lebanese air bases as it waged its largest military offensive in Lebanon since the 1982 invasion.

The attacks were the first against Lebanese military targets, and risked drawing the Lebanese army into the conflict.

Israeli fighter planes also bombed the runways of Beirut international airport, forcing it to close, and the Hezbollah television station. Meanwhile the Israeli navy imposed a blockade on Lebanese ports.

Israel's massive military operation was prompted by the abduction early yesterday of two Israeli soldiers, and the deaths of eight more, in a cross-border raid by the Islamic militia group Hezbollah. The Syrian- and Iranian-backed militant group also rained rockets into northern Israel, forcing thousands of civilians to hide in air-raid shelters.

Israel hit back with dozens of airstrikes, in which least 28 Lebanese civilians were reported to have been killed. The victims included a Shia Muslim sheikh who was killed with his wife and eight children when a missile struck their home in central Lebanon.

As Mahmoud Abbas, the Palestinian President, spoke of the risk of "a new regional war", an Israeli news website reported that Israel had warned Lebanon to evacuate all civilians from the Hezbollah-controlled southern suburbs of Beirut, where the group's leader lives.

But Hezbollah threatened to send rockets against the northern Israeli city of Haifa if southern Beirut comes under attack.

"The Islamic Resistance declares that it will shell the city of Haifa and surrounding areas if the southern suburbs and Beirut are the target of a direct Israeli aggression," the group said in a statement.

This afternoon, Israeli fighter bombers dropped two bombs on the runway at the Lebanese army's main air base at Rayak in the eastern Bekaa Valley. No casualties or damage to aircraft was reported. Later, Israeli warplanes fired four missiles at the Qoleiat air base in northern Lebanon, police said.

The Lebanese army does not have any fixed-wing aircraft but instead operates a fleet of ageing US-built helicopters. After the strike on Beirut airport, the attacks virtually cut off civil and military air access into Lebanon in an effective blockade of the country.

"Israel is imposing an air, maritime and land blockade on Lebanon until further orders as part of operations to retrieve its two soldiers abducted by Hezbollah on Wednesday," Israeli army radio announced.

The Israeli offensive was condemned by France and Russia as disproportionate. Philippe Douste-Blazy, the French Foreign Minister, said Israel's actions could "plunge Lebanon back into the worst years of the war with the flight of thousands of Lebanese who ... were in the process of rebuilding their country".

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