Dozens of people have been killed by Israeli strikes in Lebanon, including 20 who died after a strike flattened a multi-story residential building in central Beirut overnight, according to Lebanese officials.

Israeli airstrikes Saturday in central Beirut killed at least 20 people, officials said, as the once-rare attacks on the heart of Lebanon's capital continued without warning while diplomats scrambled to broker a cease-fire.

The Israel Defense Forces continued its intense airstrike and ground campaigns in Gaza -- particularly in the north of the strip -- and in Lebanon, with Israeli attacks on targets nationwide including in the capital Beirut.