Countries across Europe and the Middle East condemned Israel's resumption of airstrikes on the Gaza Strip on Tuesday.
France condemned Israeli strikes on Gaza, adding it was calling for an immediate halt to the violence, the French Foreign Affairs ministry said in a statement.
Qatar, a key mediator between Israel and Hamas, added that there was a need for Gaza ceasefire talks to resume, while also condemning the strikes.
Saudi Arabia's foreign ministry called on the international community to step in to stop what it described as crimes against the Palestinians while denouncing the airstrikes "in the strongest terms."
Germany's Foreign Minister, Anna Baerbock, commented that the end of the ceasefire due to Israeli airstrikes is "a reason for major concern."
Russia's ambassador to the UN, Vasily Nebenzya, called on the UN Security Council to do everything possible to ensure the resumption of the ceasefire, warning that the humanitarian crisis "has become truly biblical in nature."
Hamas-run Palestinian health authorities claim Israeli airstrikes killed more than 400 people, threatening the complete collapse of a two-month ceasefire as Israel vowed to use more force to free hostages held by Hamas.
OCHA statement
The UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator (OCHA)'s Tom Fletcher commented that hostilities must cease, the ceasefire must be renewed, and humanitarian aid and commercial essentials must be allowed to enter Gaza.
"Overnight our worst fears materialized. Airstrikes resumed across the entire Gaza Strip. Unconfirmed reports of hundreds of people killed ... once again, the people of Gaza are living in abject fear," Fletcher said.
"Humanitarian workers remain on the ground ... ready to provide life-saving support to survivors and to carry out humanitarian operations," Fletcher added. "We must be allowed to do so."
"This total blockade of life saving aid, basic commodities and commercial goods will have a disastrous impact on the people in Gaza who remain dependent on a steady flow of assistance into the strip," he said.
He said the ceasefire had showed what was possible and enabled aid delivery.
"We cannot and must not accept a return to pre-ceasefire conditions or the complete denial of the entry of humanitarian relief. Civilians must be protected, and their essential needs must be met. International law must be respected," he said.
"The return to hostilities overnight must cease."
'Israel is breaching int'l law by cutting off Gaza aid'
Earlier, on Monday, the UK's Foreign Secretary, David Lammy, accused Israel of "breaching international law" during a House of Commons debate, condemned Israel's halting of aid into the Strip, calling it "appalling and unacceptable" and adding that aid should never be used as a political tool.