UN Secretary-General Antonio Guterres is "extremely concerned" with the escalation of the conflict in Lebanon, his chief spokesperson said on Tuesday.

"He appeals for an immediate ceasefire. An all-out war must be avoided in Lebanon at all costs, and the sovereignty and territorial integrity of Lebanon must be respected," the spokesperson, Stephane Dujarric, said in a statement.

The spokesperson also said Guterres spoke earlier in the morning with Prime Minister Najib Mikati of Lebanon, telling Mikati that "the entire United Nations system in Lebanon is mobilized to assist all those in need in the country."