Speaking in front of the U.N. General Assembly, Guterres once again called for an immediate ceasefire by both sides, saying he was "deeply shocked by the air and artillery bombardment by the Israeli Defense Forces in Gaza," where he said at least 208 Palestinians had been killed, including 60 children.
He also urged Hamas and other militant groups to stop launching rockets and mortars "from highly populated civilian neighborhoods into civilian population centers in Israel - also in clear violation of international humanitarian law."
The 193-member U.N. General Assembly met to discuss the renewed violence, but no action was expected.
Rocket attacks on Israel stopped for eight hours on Thursday - the 11th day of hostilities - before resuming against communities near the Gaza border and the city of Beersheba.
Israel continued air strikes in Hamas-run Gaza, saying it wanted to destroy the Islamist militant group's capabilities and deter it from future confrontation after the current conflict.