Two rockets have struck the Israeli city of Haifa, hours after a threat by the militant Lebanese group Hezbollah.
Hezbollah has fired dozens of rockets into northern Israel
Hezbollah denied firing any rockets at the northern port - Israel's third largest city. There were no reports of injuries or damage.
Later, Lebanon's international airport was hit for a second time as Israel continued attacks by land, sea and air.
About 50 people have died in the Israeli raids, launched after Hezbollah captured two Israeli soldiers.
Most of the dead are civilians.
The fresh attacks on Beirut airport set at least one fuel tank ablaze.
The airport was already closed following Israeli air strikes earlier on Thursday.
Hezbollah had said it would attack Haifa if Israeli planes bombed Beirut.
It had fired dozens of rockets into Israel in the past two days, killing at least two Israelis and injuring dozens.
But until the Haifa attack none had gone further than 20km (12 miles) inside the country.
Haifa is more than 30km (18 miles) from the Lebanese border and had been thought to be out of Hezbollah's range.
Israeli police said two rockets had fallen on a Christian area of Haifa called Stella Maris.
The Israeli ambassador in Washington, Danny Ayalon, described the Haifa incident as a "major escalation" of the crisis.
He said the international community should make it clear to Iran and Syria - who both have links with Hezbollah - that they were "playing with fire".
Meanwhile the UN Security Council has arranged an emergency meeting for Friday at Lebanon's request.
Lebanese ministers have called for a ceasefire with Israel, saying that all means should be used to end "open aggression" against their country.
ISRAEL IN LEBANON
March 1978: Israel invades to stop Palestinian attacks
1982: Full-scale invasion; Israel occupies Beirut; pro-Israel militias massacre Palestinian refugees
May 1983: Israel pulls back, but keeps "security zone"
February 1992: Israeli air strike kills Hezbollah leader
1996: Israel launches "Grapes of Wrath" raids on Hezbollah; 100 civilians die under Israeli shelling of UN base at Qana
May 2000: Israel withdraws troops from Lebanon
January 2004: Prisoners-bodies swap agreed between Hezbollah and Israel
International calls for restraint are growing, with Russia, France and the EU saying Israel's response to the capture of two soldiers was disproportionate.
US President George W Bush described Hezbollah as a "group of terrorists who want to stop the advance of peace".
Speaking in Germany, he said Israel had the right to defend itself, but its action should not weaken the Lebanese government.
Israeli government spokesman Mark Regev said Israel was responding to "an unprovoked act of aggression" by Lebanon.
The offensive follows a day of heavy fighting in which the Israelis suffered their worst losses on the border for several years.
Eight soldiers were killed and two were injured, in addition to the two captured in a Hezbollah ambush.
The operation comes as Israel continues a separate offensive in the Gaza Strip. An Israeli soldier was captured in a cross-border raid into Israel by Palestinian militants from Gaza last month.
ISRAEL BLOCKADES LEBANON
Two rockets hit Israeli city of Haifa on Thursday evening
Israel targets Lebanon by land, air and sea: enforcing naval blockade, bombing Beirut airport and shelling Lebanese towns
Jets bomb Lebanese army air base at Rayak and Baalbek TV transmitter in Bekaa Valley
Shelling from both sides is heaviest over Lebanon's southern border
Hezbollah targets Kiryat Shmona, Nahariya and Safed in Israel