By Michelle Nichols

UNITED NATIONS (Reuters) -U.N. Secretary-General Antonio Guterres on Wednesday warned that the Gaza Strip was in the midst of an "epic humanitarian catastrophe," as calls grew for a ceasefire to replace the temporary truce between Israel and Palestinian Hamas militants.

"Intense negotiations are taking place to prolong the truce – which we strongly welcome - but we believe we need a true humanitarian ceasefire," he told a meeting of the U.N. Security Council, chaired by China's Foreign Minister Wang Yi because China is president of the 15-member council for November.

Last-minute talks continued between Israel and Palestinian militants Hamas on Wednesday to extend a truce in Gaza.

"We should work for a comprehensive and lasting ceasefire with the greatest urgency," Wang told the council. "There is no firewall in Gaza either. Resumed fighting would only, most likely, turn into a calamity that devours the whole region."

Saudi Arabia's Foreign Minister Prince Faisal bin Farhan Al Saud - standing with counterparts from Egypt, Qatar, Jordan, Turkey, Indonesia and Malaysia - told reporters at the United Nations that aid entering Gaza was "far less than is needed."

"The danger is that if ... this truce expires we will return to the killing at the scale that we have seen, which is unbearable," he said. "So we are here to make a clear statement that a truce is not enough. What is needed is a ceasefire."

Addressing the Security Council, Israel's U.N. Ambassador Gilad Erdan accused the ministers of supporting "a terror organization that aims to annihilate Israel."

"Anyone who supports a ceasefire basically supports Hamas continued reign of terror in Gaza. Hamas is a genocidal terror organization - they don't hide it - not a reliable partner for peace," Erdan said.

CIVILIAN PROTECTION

Israel says Hamas militants killed 1,200 people and took about 240 hostage in a surprise assault on Oct. 7. Israel has focused its retaliation against Hamas in Gaza, bombarding it from the air, imposing a siege and launching a ground assault.

U.S. Ambassador to the U.N. Linda Thomas-Greenfield said everything possible must be done to scale up aid and protect civilians, including U.N. staff and journalists.

"The United States has urged Israel to take every possible measure to prevent civilian casualties as it exercises its rights to safeguard its people from acts of terror," she told the Security Council, adding that Hamas' use of civilians as human shields "does not lessen Israel's responsibility."

More than 15,000 people are confirmed killed, some 40% of them under the age of 18, according to Palestinian health authorities deemed reliable by the United Nations. Many more are feared buried under the ruins.

"The truce must become a ceasefire, a permanent ceasefire. The massacres cannot be allowed to resume," Palestinian Foreign Minister Riyad al-Maliki told the Security Council.

"Our people are faced with an existential threat. Make no mistake about it. With all the talk about the destruction of Israel, it is Palestine that is facing a plan to destroy it, implemented in broad daylight," he said.

Guterres briefed the Security Council on the implementation of a resolution it adopted earlier this month that called for humanitarian pauses in fighting to allow aid access and the release of all hostages held by Hamas.

The United Nations has scaled up the delivery of humanitarian aid to Gaza - a coastal enclave of 2.3 million people - during the truce, but Guterres said the level of aid "remains completely inadequate to meet the huge needs."

"The people of Gaza are in the midst of an epic humanitarian catastrophe before the eyes of the world," he said. "We must not look away."

(Reporting by Michelle Nichols; editing by Kanishka Singh and Deepa Babington)