Israeli Prime Minister Benjamin Netanyahu warned Lebanese people to move away from danger as Israel pounded Hezbollah targets in the country's south and east on Monday.

"Please, get out of harm's way now. Once our operation is finished, you can come back safely to your homes," Netanyahu said in a video statement shortly after the Israeli army announced it had struck 800 Hezbollah targets in Lebanon.

A source close to Hezbollah said an Israeli strike on Beirut's southern suburbs on Monday targeted the group's commander for south Lebanon, where the movement has clashed with Israel for nearly a year.

"The target of the Israeli strike was Ali Karake, the current commander of the southern front and the third-in-command after" two top commanders who were both killed in Israeli strikes in the southern suburbs in recent weeks, said the source requesting anonymity to discuss sensitive matters.

Israel is bombing targets across many parts of Lebanon, striking senior militants in Beirut's southern suburbs and apparently hiding bombs in pagers and walkie-talkies. Hezbollah is firing rockets and drones deep into northern Israel, setting buildings and cars alight.

But no one is calling it a war — not yet.

Israeli Prime Minister Benjamin Netanyahu said on Monday that the military was changing the "security balance" along the northern border after launching the deadliest strikes on south Lebanon since fighting started last October.

"I promised we would change the security balance, the balance of power in the north –- and that is exactly what we are doing," Netanyahu said during a security meeting, adding that Israel's policy was to preempt threats rather than "wait" for them.

French presidential envoy for Lebanon Jean-Yves Le Drian will arrive in Beirut on Monday, media reports said.

The United Nations voiced alarm Monday at the escalating violence between Israel and Hezbollah in Lebanon, warning that actions and rhetoric was catapulting the Mideast conflict "to another level".

"We are extremely concerned, deeply worried about the escalation in Lebanon," Ravina Shamdasani, spokeswoman for the UN rights office, told AFP.

Iran's foreign ministry warned Israel on Monday of "dangerous consequences" following deadly strikes on Hezbollah strongholds in Lebanon.

Foreign ministry spokesman Nasser Kanani called the Israeli strikes "insane", and warned of "the dangerous consequences of the Zionists' new adventure".

Thousands of people are leaving south Lebanon and heading north after Israel intensified airstrikes on Monday, leaving 100 people dead and hundreds wounded.

In the southern port city of Sidon, the main north-south highway was packed with cars heading north in the direction of the capital Beirut.

State-run Lebanese media said Israel was conducting new raids across Lebanon's east Monday, hours after deadly strikes on the south and east, in the deadliest single day in nearly a year of cross-border clashes.

"Enemy raids targeted the mountain" areas in the Baalbek region and several towns and villages, the National News Agency said, adding that "the Israeli enemy" launched a strike on the town of Hermel.

The United Nations Special Coordinator for Lebanon, Jeanine Hennis-Plasschaert, begins an official visit to Israel today, Monday, her office said.

She is set to meet with senior Israeli officials to discuss recent developments, the office said in a statement.