Israel has launched its first major offensive in Lebanon since 2000.

Israel Air Force F-15 and F-16 fighter-jets struck suspected Hizbullah strongholds in such cities as Beirut and Tyre as well as missile arsenals throughout southern Lebanon. The Iranian-sponsored Hizbullah has an estimated 15,000 missile and rockets and has threatened to fire long-range weapons toward Tel Aviv.

“This is a different story than in the past,” a senior military source said. “We’re not talking any longer of a battle of a day or two. This will take a long time.”

The source said Israel’s military, which withdrew in 2000, has imposed an air, sea and land blockade on Lebanon. He said this was a major element in Israel’s retaliation for the Hizbullah strike on northern Israel on Wednesday, in which seven soldiers were killed and two others were captured.

Hizbullah struck from positions along the Israeli border damaged in a military strike in May At the time, the Israeli government dismissed a military recommendation to prevent Hizbullah from refurbishing the outposts.

“We don’t intend to allow Hizbullah to return to our borders,” Defense Minister Amir Peretz said on Thursday. “The Lebanese Army must be deployed there.”

Israel, however, has not sent a major ground force in Lebanon. The source said the military has recommended that the offensive remain limited to air strikes, including the destruction of the homes of Hizbullah leaders in southern Beirut.

“To clear the area, you need infantry,” former Israel Air Force commander Maj. Gen. Eitan Ben-Eliyahu said. “The area is large. The name of the game is to be in the area all the time.”

Lebanese sources reported 26 people killed in Israeli air strikes overnight Thursday. They said 20 bridges in southern Lebanon were also destroyed. There were no reports of Hizbullah firing anti-aircraft missiles.

“The government was not aware of and does not take responsibility for, nor endorses what happened on the international border,” Lebanese Prime Minister Fuad Siniora said after an emergency Cabinet meeting on Wednesday.

In response, Hizbullah launched dozens of Soviet-origin Katyusha rockets toward northern Israel. At least one Israeli was killed and another 30 were injured in the Israeli city of Nahariya.

“There will be difficult days,” Israeli Justice Minister Haim Ramon said.

Military sources said Hizbullah fired rockets toward an air force base at Meron, which contains an air command facility. The sources said the base was damaged but nobody was injured.

The Hizbullah rocket fire has paralyzed much of northern Israel. Residents have been ordered to remain in bomb shelters and train service was suspended.

“We’re going to have to absorb in the short-term so we could defend ourselves in the future,” Maj. Gen. Yitzhak Gershon, head of the military’s Home Front Command, said.

At this point, Hizbullah has been striking targets at a range of up to 25 kilometers, the sources said. But they said Hizbullah could escalate by firing the Iranian-origin Fajr-4 and Fajr-5 rockets, which could reach the Tel Aviv area.

The immediate threat, the sources said, was a Hizbullah strike on Haifa.

Haifa is the third largest city in the country and contains a naval port and chemical plant.

“I estimate that this is indeed a realistic scenario,” Dan Scheuftan, a senior researcher of the National Security Studies Center at Haifa University, said.