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.

Grand Ayatollah Ali Sistani, Shiite Islam's highest authority in Iraq, appealed Monday for "every possible effort" to end Israeli "aggression" against Lebanon.

Sistani called for "the exercise of every possible effort" to end this "barbaric aggression and to protect the Lebanese people."

A missile hit the al-Wardiyet area between the Jbeil district towns of Almat and Ehmej on Monday, as Israeli warplanes targeted Lebanon’s western mountain range.

Hezbollah said it targeted three sites in northern Israel including military production facilities in retaliation for intense Israeli strikes on south and east Lebanon.

"In response to the Israeli enemy attacks that targeted the south and Bekaa areas", Hezbollah fighters bombed two north Israel military positions as well as the "Rafael defense industry complexes" north of the city of Haifa, the group said in a statement.

An Israeli military official said Israel is focused on aerial operations and has no immediate plans for a ground operation.

The official, speaking on condition of anonymity in keeping with regulations, said more than 300 strikes on Lebanon's south and east on Monday are aimed at curbing Hezbollah's ability to launch more strikes into Israel.

The Kremlin on Monday said that the threat of escalation of attacks by Israel and Hezbollah was a matter of the utmost concern for Russia.

"The situation is swiftly deteriorating every day. Tension is growing, unpredictability is increasing. This is a matter of extreme concern for us," Kremlin spokesman Dmitry Peskov told journalists.

Caretaker Prime Minister Najib Mikati denounced a "destructive plan" amid intense Israeli strikes Monday on east and south Lebanon and as Israel's military said it attacked some 150 Hezbollah targets.

"The continuing Israeli aggression on Lebanon is a war of extermination in every sense of the word and a destructive plan that aims to destroy Lebanese villages and towns," Mikati told a cabinet meeting. He urged "the United Nations and the General Assembly and influential countries... to deter the (Israeli) aggression".