CAIRO, Egypt — Israel appears to be attempting to cripple or dismantle Hezbollah’s base in southern Lebanon, where it has operated freely since Israeli troops withdrew in 2000.

In the first full day of Israel’s Lebanon offensive, the Jewish state laid siege to its northern neighbor, cutting it off from the outside world, sealing its ports with warships, and bombing the airport and the road to Damascus, Syria.

Hezbollah hit back yesterday, launching Katyusha rockets into northern Israel, including a volley that hit the city of Haifa. The shelling of Israel’s third-largest city prompted an official in the Israeli prime minister’s office, David Baker, to say Hezbollah would “pay a heavy price” for its actions, according to the Associated Press.

Israel has said publicly that the purpose of the offensive in Lebanon was to find two soldiers that Hezbollah abducted on Wednesday, Ehud Goldwasser and Eldad Regev, and prevent them from being smuggled into Syria or flown to Iran. But the scale of the fighting suggested that ending the threat of Hezbollah is a war aim.

Israeli jets yesterday and early Friday bombarded Hezbollah positions deep in the Bekaa Valley, the terrorist organization’s center of operations, where many of its training camps and gun depots are based. Jets also dropped leaflets on Beirut neighborhoods warning Lebanese citizens to avoid areas where Hezbollah is known to operate.

World leaders yesterday fretted that the rapidly escalating conflict between Lebanon and Israel could spin into a wider regional war. The United Nations announced that it was sending its special envoy for the Middle East, Terje Roed Larsen, and a U.N. special political adviser, Vijay Nambiar, to Cairo on Friday and then to Syria, Israel, and Lebanon.

In Germany, President Bush reiterated his view that Israel had a right to defend itself, but he warned against any actions that would destabilize the Lebanese government. A European Union statement criticized the Jewish state for its disproportionate use of force.

The response from the markets to Israel’s two-front war sent oil prices to record highs of more than $78 a barrel. Stock exchanges in Beirut, Cairo, and Tel Aviv all suffered losses, with Israel’s benchmark stocks suffering the worst two-day loss since the start of the second Palestinian Arab intifada in 2000.

At Turtle Bay, America beat back a proposed U.N. Security Council resolution sponsored by Qatar that called on Israel to remove its troops from Lebanon and Gaza. In his speech rejecting the proposal, America’s ambassador the United Nations, John Bolton said: “Establishing the foundations for a lasting peace, however, will require us to focus our attention not just on Hamas, but on the state sponsors of terror who back them, particularly Syria and Iran. Let us be clear that without the financial and material support of Damascus and Tehran, Hamas would be severely crippled in carrying out its terrorist operations.”

Syria was president of the Security Council in 2003 when that body passed what America and Britain said was the last resolution requiring Iraq to disarm.

In Tehran yesterday, President Ahmadinejad warned that any Israeli strike on Syria would be seen as an attack on the entire Islamic world. State television quoted the president’s statement from a telephone call with Syria’s president, Bashar Assad.

“If the Zionist regime commits another stupid move and attacks Syria, this will be considered like attacking the whole Islamic world, and this regime will receive a very fierce response,” Mr. Ahmadinejad said. Israeli fighters buzzed Mr. Assad’s summer palace on June 29 in response to the Hamas kidnapping of Corporal Gilad Shalit.

A Hezbollah spokesman said yesterday that the soldiers it kidnapped on Wednesday were taken to a faraway location and that Israel’s hunt for them in Lebanon would be fruitless. The deputy director of Israel’s Foreign Ministry, General Gideon Meir, said his government had specific information that the soldiers would be taken to Iran. Iran’s Foreign Ministry denied this.

Secretary of State Rice said yesterday that the world was putting its faith in the U.N. mission led by Messrs. Nambiar and Roed Larsen. Mr. Roed Larsen warned the State Department six years ago that Hezbollah was amassing shoulder-held rockets in its Bekaa bases.

The Associated Press yesterday put the number of casualties in Lebanon at more than 50.