Israel widened its air strikes in Lebanon on Wednesday and Lebanon's health minister reported at least 51 people were killed and at least 223 wounded in Wednesday's strikes.
Israel shot down a missile that the Hezbollah movement said it had aimed at the headquarters of the Mossad intelligence agency near Israel's biggest city, Tel Aviv.
Israeli officials said a heavy missile had headed towards civilian areas in Tel Aviv, not the Mossad HQ, before being shot down.
"You hear the jets overhead; we have been striking all day," General Herzi Halevi told Israeli troops on the border with Lebanon, according to a military statement.
"This is both to prepare the ground for your possible entry and to continue degrading Hezbollah."
World leaders meanwhile expressed concern that the conflict - running in parallel to Israel's war in the Gaza Strip against Hamas - was rapidly intensifying as the death toll in Lebanon rose and thousands of people fled their homes.
Hezbollah has been accused of launching rockets at houses in northern Israel. (AP PHOTO)
US Secretary of State Antony Blinken said his country and its allies were working tirelessly to avoid a full-blown war between Israel and Hezbollah.
"Risk of escalation in the region is acute ... The best answer is diplomacy, and our co-ordinated efforts are vital to preventing further escalation," Blinken said at a meeting with Gulf Arab state officials and ministers in New York.
Israeli air strikes this week have targeted Hezbollah leaders and hit hundreds of sites deep inside Lebanon while the group has fired barrages of rockets into Israel.
Wednesday morning's Hezbollah strike was the first time since the war broke out last October that one of its missiles had been sighted above Tel Aviv - Israel's commercial hub and seen as a target with the potential to trigger an escalation in Israeli action.
Hundreds of thousands of Lebanese have fled their homes and hospitals have filled with the wounded since an intensification of bombing on Monday, when more than 550 people were killed in Lebanon's deadliest day since the end of a 1975-1990 civil war.
There was no let up on Wednesday.
Israel said its warplanes were carrying out extensive strikes in south Lebanon and the Bekaa Valley, a Hezbollah stronghold further north.
Israeli officials said the missile fired at Tel Aviv was shot down with a David's Sling missile, a surface-to-air missile designed to destroy tactical ballistic missiles at low altitude.
Hezbollah blamed Mossad for assassinations of its leaders.
It has also accused the spy agency of carrying out an operation last week in which booby-trapped pagers and radios of Hezbollah members exploded, killing 39 people and wounding nearly 3000.
Israel has neither confirmed nor denied involvement.
Israel has expanded the zones it has been striking since Tuesday night, with attacks for the first time on the beach resort town of Jiyyeh just south of Beirut and Maaysrah.
The strikes also took place in Bint Jbeil, Tebnin and Ain Qana in the south, the village of Joun in the Chouf district near the southern city of Sidon, and Maaysrah in northern Keserwan district.
As many as half a million people may have been displaced in Lebanon, its foreign minister said.
In Beirut, thousands of displaced people who fled from southern Lebanon were sheltering in schools and other buildings.
More than 60 people were relocated by the Lebanese Army early on Wednesday from the Christian town of Alma Chaab, along the border with Israel, following strikes overnight.
