UN secretary-general Antonio Guterres said he deeply regretted the resumption of hostilities between Israel and Hamas in the Gaza Strip on Friday and hoped a truce could be re-established.
Fighting resumed in Gaza on Friday immediately after the expiry of a week-long truce between Hamas and Israel, with the first fatalities reported minutes later, according to health officials in the Palestinian territory.
"I deeply regret that military operations have started again in Gaza," Guterres said on X, formerly Twitter.
"I still hope that it will be possible to renew the pause that was established. The return to hostilities only shows how important it is to have a true humanitarian ceasefire."The truce had paused fighting that began on October 7 when Hamas militants
broke through Gaza's militarised border into Israel.
The unprecedented attack killed about 1,200 people, mostly civilians, and militants kidnapped about 240, according to Israeli authorities.
Israel vowed in response to eliminate Hamas and unleashed a relentless air and ground military campaign in Gaza that the territory's Hamas government says has killed more than 15,000 people, also mostly civilians.
The United Nations children's agency UNICEF condemned the resumption of
fighting, saying: "Today, those in power have decided that the killing of children would recommence."
"The humanitarian situation in Gaza is so perilous that anything other than sustained peace and at-scale emergency aid will mean catastrophe for the children of Gaza," UNICEF spokesman James Elder told reporters in Geneva via video-link from the besieged Palestinian enclave.
Elder said the "dire" state of health, nutrition, water and sanitation there threatened to trigger "a disaster of unparallelled magnitude for the children of Gaza".
"Inaction, at is core, is an approval of the killing of children," he said, calling it "reckless to think more attacks on the people of Gaza will lead to anything other than carnage."
"It's deeply unsettling to hear how some have been able to overlook the tragic deaths of these children; and now, today, are seemingly comfortable with the horrors -- the attacks -- starting again," he said.
"To accept the sacrifice of the children in Gaza is humanity giving up.
"This is our last chance before we delve into yet again explaining why
another entirely avoidable tragedy was not stopped."
Elder said that he visited children in the Nasser hospital in Khan Yunis inthe southern Gaza Strip as hostilities resumed on Friday.
He said that during the truce, "slowly, slowly, glimpses of childhood started to come back" to traumatised and wounded children.
However, as the explosions began, "in an instant... you saw fear return and childhood retreat", he said.