Israel launched a new air and ground offensive in northern Gaza Sunday, hours after pounding Beirut's southern suburbs in the heaviest bombardment since it stepped up its pursuit of Hezbollah last month.

The intensified campaign on two fronts, including an overnight strike on a Gaza mosque that killed 19, came as Israel remained on high alert ahead of memorial events to mark the surprise attack a year ago that triggered the ongoing war.

In just over a week, intensified Israeli strikes in Lebanon killed seven high-ranking commanders and officials from the powerful Hezbollah militant group, including the group's leader, Sayyed Hassan Nasrallah.

The move left Lebanon and much of the Mideast in shock as Israeli officials celebrated major military and intelligence breakthroughs.

Israel's assassination of Hezbollah leader Sayyed Hassan Nasrallah is a monumental and hugely demoralizing blow to the group he led for 32 years, marking a significant inflection point for Lebanon and the region.

Hezbollah's announcement of his death Friday triggered tears and celebrations across the Arab world, pointing to the widespread reach and influence of a divisive man who has been at the forefront of Middle Eastern politics for decades.

Sayyed Hashem Safieddine, a potential successor to his slain cousin Sayyed Hassan Nasrallah, is one of Hezbollah's most prominent figures and has deep religious and family ties to group's patron Iran.

Safieddine bears a striking resemblance to his charismatic maternal cousin Nasrallah but is several years his junior, aged in his late 50s or early 60s.

Middle East nations and Hezbollah's allies in the Tehran-aligned "Axis of Resistance" reacted on Saturday to the killing of Sayyed Hassan Nasrallah after the Lebanon-based group confirmed their leader's death in Israeli strikes.

Military officials in Israel announced on Saturday morning that Nasrallah, who headed Hezbollah for more than three decades, died in bombardment targeting the group's headquarters in the southern suburbs of Beirut Friday night.

In 2006, after a bruising monthlong war between Israel and Lebanon's powerful Hezbollah, the United Nations Security Council unanimously voted for a resolution to end the conflict and pave the way for lasting security along the border.

But while there was relative calm for nearly two decades, Resolution 1701's terms were never fully enforced.

Israel and Hezbollah each have strong incentives to heed international calls for a cease-fire that could avert all-out war — but that doesn't mean they will.

Hezbollah is reeling after a sophisticated attack on personal devices killed and wounded hundreds of its members. Israeli airstrikes have killed two top commanders in Beirut in less than a week, and warplanes have pounded large parts of Lebanon, killing over 600 people.

When she first heard about the evacuation warnings Israel was sending to residents of Lebanon, Aline Naser's thoughts immediately turned to Gaza.

For the past year, the 26-year-old Beirut resident has been following with horror the reports about besieged Palestinians in the Gaza Strip ordered to move from one place to the other, fleeing to "humanitarian zones" only to be bombed and ordered to leave again.

By Mireille Rebeiz, Dickinson College

Lebanese families have been fleeing the country's south in the thousands amid escalating tensions and an Israeli bombardment that has so far killed hundreds.

Fadi, a type of rocket used for the first time by Hezbollah against Israel, has more explosive power and range than rockets deployed previously, but lacks precision, experts say.