"More than 50,000 Lebanese and Syrians living in Lebanon have now crossed into Syria fleeing Israeli air strikes," Filippo Grandi said on X.

He added that "well over 200,000 people are displaced inside Lebanon".

A UNHCR spokesman said the total number of displaced in Lebanon had reached 211,319, including 118,000 just since Israel dramatically ramped up its air strikes on Monday.

The remainder had fled their homes since Hezbollah militants in Lebanon began low-intensity cross-border attacks a day after its Palestinian ally Hamas staged its unprecedented attack on Israel on October 7, triggering war in the Gaza Strip.

Israel has shifted the focus of its operation from Gaza to Lebanon, where heavy bombing has killed more than 700 people, according to Lebanon's health ministry, as cross-border exchanges escalated over the past week.

Most of those Lebanese deaths came on Monday, the deadliest day of violence since Lebanon's 1975-1990 civil war.

"Relief operations are underway, including by UNHCR, to help all those in need, in coordination with both governments," Grandi said.