UNITED NATIONS - Iran on Saturday called on the UN Security Council (UNSC) to convene an emergency meeting to address the latest situation in Lebanon.

"I am writing to urgently bring to your attention, and that of members of the Security Council, the latest cruel acts against Lebanon," Iran's permanent representative to the United Nations Amir Saeid Iravani said in a letter to UN Secretary-General Antonio Guterres and Samuel Zbogar, president of the Security Council for September.

Denouncing Israel's devastating airstrikes on Beirut's southern suburbs that killed Hezbollah leader Sayyed Hassan Nasrallah as "a flagrant act of terrorist aggression," he said that Israel's "brazen acts of aggression" pose a grave threat to regional and international peace and security, pushing the entire region into an all-out catastrophe.

Given the grave consequences on regional and international peace and security, Iran called on the Security Council to unequivocally condemn Israel's actions in the strongest possible terms, he said.

Also on Saturday, the spokesman for UN Secretary General Antonio Guterres said he is gravely concerned by the dramatic escalation of events in Beirut in the last 24 hours.

"This cycle of violence must stop now, and all sides must step back from the brink," Stephane Dujarric, spokesman for the secretary general, said in a statement.

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"The people of Lebanon, the people of Israel, as well as the wider region, cannot afford an all-out war," the statement said.

It added that the UN chief "urges the parties to re-commit to the full implementation of Security Council resolution 1701 (2006) and immediately return to a cessation of hostilities. He also reiterates his call for an immediate ceasefire in Gaza and the release of all hostages held there."