Israeli forces struck Beirut's international airport for the second time Thursday, hitting fuel tanks that exploded into fireballs.
The attack came soon after two rockets struck the northern Israeli port of Haifa on a day of spiraling violence and deepening crisis.
Israel Defense Forces said the Haifa rockets came from Lebanon and blamed Hezbollah, whose guerrillas abducted two soldiers and killed eight others one day ealier.
The violent aftermath has claimed the lives of 45 Lebanese civilians and two soldiers, according to the Lebanese health ministry.
Subsequent Hezbollah rocket attacks have killed at least two Israelis and wounded 50, according to Israeli ambulance services and police.
Daniel Ayalon, the Israeli ambassador to the United States, said the Haifa attack was "a major, major escalation."
"It goes to show that there is no timetable," Ayalon said during a speech in Washington. "We will have to continue with the operation until there is no capability of the Hezbollah to do what they are doing."
Hezbollah, meanwhile, says it has a right to remain on "any part of Lebanese soil."
"We intend to send a clear message that we wish not to escalate this conflict by killing civilians," said Naim Qasem, Hezbollah's deputy secretary-general. "But we know that Israel will not stop its aggression until it feels pain. Therefore, they should learn from what happened today. They have failed to protect their cities and their civilians."
Hezbollah earlier had threatened to hit Haifa, but Lebanese TV reported that the militant group denied launching the attack on the city of 280,000.
Ambulance services said no one was hurt in the attack, which -- if confirmed -- would be the first time Hezbollah rockets have hit so deeply into Israeli territory.
Earlier Thursday, Israel's warplanes bombed Beirut's international airport for the first time and its navy began a blockade of Lebanon's ports.
Hundreds of targets between the southern border and the capital were attacked, the IDF said.
Hezbollah guerrillas fired scores of rockets from Lebanon into northern Israel in the most intense bombardment in years.
Lebanon also said 103 people were hurt by the Israeli attacks, The Associated Press reported.
One rocket attack Thursday on the northern Israeli town of Nahariya hit a group of journalists, the AP said.
Both Israel and Lebanon have said the violence amounts to acts of war.
Israeli Prime Minister Ehud Olmert called the attacks and abductions an "act of war" and blamed the Lebanese government, which he said would be held responsible for the two soldiers' safe release.
Lebanese Interior Minister Ahmed Fatfat called Israel's retaliatory attack on Beirut airport a "general act of war," saying the strikes had nothing to do with Hezbollah but were instead an attack against the country's "economic interests," especially its tourism industry.
Beirut's Rafik Hariri International Airport was forced to close after Israeli fighter jets hit all three of its runways, leaving huge craters that made them unusable. All flights have been diverted.
Two other Lebanese airports were attacked Thursday morning, the IDF said.
The Israeli military gave no details, but Lebanese army sources said that the Rayak Air Base in the Bekaa Valley near the Syrian border had been hit as well as a small military airport in Qulayaat in northern Lebanon.
Israel said it targeted the international airport because it was a transfer point for weapons and supplies to Hezbollah.
Israeli warships set up a blockade, preventing cruise ships from docking in the Lebanese capital and cutting off the delivery of fuel to operate Lebanese power plants.
The roar of Israeli warplanes could be heard over the main transportation route between Lebanon and Syria, and witnesses said hundreds of tourists were lined up on the Syrian border, trying to get out of Lebanon.
Lebanese Information Minister Ghazi Aridi called for a comprehensive cease-fire, saying the Lebanese government had nothing to do with the Hezbollah attacks.
An adviser to Lebanese Prime Minister Fuad Sinora, Mohamad Chatah, said the country's fledgling government has struggled to assert its authority since Syria withdrew its troops last year.
"No question that we are against this kind of violence," Chatah said. But he added, "Many people in Lebanon have very strong views against what Israel has been doing."
After Israel's airport strike, planes began dropping leaflets warning residents of an impending attack on an area of southern Beirut where Hezbollah leader Hassan Nasrallah is believed to live.
Israel: 'We mean business'
Palestinian Authority President Mahmoud Abbas said Thursday he fears a "regional war is mounting" with Israel's military campaigns in Lebanon and Gaza, where forces were deployed after last month's capture of an Israeli soldier.
"This is not our interest and will not bring peace and stability to the region," Abbas said, referring to "this [Israeli] aggression."
President Bush said all countries had a right to defend themselves but warned Israel to take care not to "weaken" Lebanon's government.
Bush also stressed during a visit to Germany that Syria "needs to be held to account."
Hezbollah enjoys substantial backing from Syria and Iran and is considered a terrorist organization by the United States and Israel. The group holds posts in Lebanon's government.
Israeli Security Cabinet Minister Isaac Herzog said: "We are taking strong measures so that it will be clear to the Lebanese people and government ... that we mean business."
The United Nations will send a team to the Middle East to urge both sides to use restraint, a spokesman for Secretary-General Kofi Annan said Thursday.
The Security Council will hold an "urgent meeting" Friday at the request of Lebanon to address the escalating tensions, France's U.N. ambassador Jean-Marc de La Sabliere said Thursday.
Israeli airstrikes were aimed at targets used by Hezbollah for storing weapons, the IDF said.
Warplanes also hit the al-Manar television station, because Hezbollah uses it to incite and recruit activists, the IDF said. A broadcast tower was destroyed and three people were injured, but the station was able to continue broadcasting, al-Manar Editor Ibrahim Moussawi said.
Israel's Cabinet authorized a "severe and harsh" response to the abduction of two soldiers, identified Thursday as Ehud Goldvasser, 31, from Nahariya, and Eldad Regev, 26, from the Haifa suburb of Kiryat Motzkin.
Hezbollah called for a prisoner exchange, but Israel has rejected the call.
Hezbollah chief Nasrallah told reporters that seizing the soldiers was "our natural, only and logical right" to win freedom for Hezbollah prisoners held by Israel.
Nasrallah said the two soldiers had been taken to a place "far, far away" and that an Israeli military campaign would not win their release.
CNN's Barbara Starr and John Vause and journalist Anthony Mills in Beirut contributed to this report.