The Israel Defense Forces (IDF) is telling all civilians to evacuate Gaza City, calling for about 1 million Palestinians to move south for their own safety and the safety of their families, with the U.N. warning the move risked devastating humanitarian consequences, according to Politico. 

The evacuation call comes amid growing expectations that Israel is set to launch a ground assault on Gaza, as it seeks to wipe out Hamas militants in the wake of last weekend’s devastating attacks, which killed 1,300 Israelis. Dozens of people were kidnapped and taken to Gaza.

Officials in Gaza say more than 1,500 people have been killed there in Israel’s retaliatory strikes, and Palestinians protest Israel’s ultimate goal is to press Gazans into Egypt. Hamas, the Islamist party which rules Gaza, called on people not to flee. Al Jazeera cited the Hamas Authority for Refugees telling residents in the north to “remain steadfast in your homes and to stand firm in the face of this disgusting psychological war waged by the occupation.”

The Israeli forces say they need civilians to leave to avoid casualties as they ramp up their attack on Hamas — which has told Palestinians to stay in place.

The United Nations called on Israel to reverse course, with a spokesperson saying the evacuation “could transform what is already a tragedy into a calamitous situation.”

“The United Nations considers it impossible for such a movement to take place without devastating humanitarian consequences,” said Stéphane Dujarric, a spokesperson for U.N. chief António Guterres.

Meanwhile, Egypt is resisting calls for it to allow civilians to flee Gaza across its border through the Rafah crossing, with President Abdel Fattah El-Sisi telling Palestinians to “stay steadfast and remain on [their] land.”

Israel’s former National Security Adviser Eyal Hulata called on Egypt “to bear responsibility.” In an interview with Politico, Hulata said civilians ought to be able to leave via the Rafah crossing, which is policed by Egyptian border guards. “Egypt is right there and they can absorb [refugees] into Egypt and to Sinai. Temporarily of course, because Israel does not aim at the conquering of the Gaza Strip.”

The United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA), meanwhile, announced it had “relocated its central operations centre and international staff to the south” of Gaza. “We urge the Israeli Authorities to protect all civilians in @UNRWA shelters including schools,” the agency said on social media.

Against that backdrop, European Parliament President Roberta Metsola and Commission chief Ursula von der Leyen are set to touch down in Israel mid-morning Friday, “to express solidarity with the victims of the Hamas attacks, and meet with Israeli leadership,” according to a social media post.

The details of the one-day trip, which comes after an invitation from the Knesset, are yet to be released, but Metsola is expected to highlight the need to establish humanitarian corridors and safeguard critical civilian infrastructure in Gaza, as Israel mounts its response to the attacks.

The U.N. humanitarian office (OCHA) said early on Friday that more than 400,000 people had fled their homes in the Gaza Strip and 23 aid workers had been killed since the start of Israeli retaliatory strikes in response to a deadly Hamas incursion, according to Reuters.

The agency launched an appeal for nearly $294 million to help some 1.3 million people in Gaza and the West Bank, of which nearly half was programmed for food aid as supplies run out.

“Mass displacement continues. In the Gaza Strip, the cumulative number of internally displaced persons (IDPs) increased by 25% over the past 24 hours, now exceeding 423,000, of whom over two thirds are taking shelter in UNRWA schools,” OCHA said, referring to the U.N. Palestinian refugee agency.

It said 23 aid workers had so far been killed since the weekend, including 11 health workers and 12 UNRWA employees.