Hundreds of people are reported to have died in a massive explosion at a hospital in Gaza City, on the eve of Joe Biden’s arrival for a visit that was intended to fend off the humanitarian disaster in Gaza and prevent the conflict escalating into a regional war. The Gaza health ministry, which is run by Hamas, claimed that more than 500 people had been killed an Israeli airstrike on the al-Ahli Arabi Baptist hospital which, if confirmed, would make it the deadliest single bombing of all the five wars Israel and Hamas have fought over Gaza. An official from the Gaza civil defence said more than 300 people had been killed in the blast. The Israeli military denied responsibility, suggesting the hospital was hit by a rocket barrage launched by the Palestinian Islamic Jihad militant group. Islamic Jihad also denied responsibility, saying: “The occupation is trying to cover for the horrifying crime and massacre they committed against civilians.” The bombing of the hospital threw a dark shadow over Biden’s visit on Wednesday, which was already the most difficult and critical foreign trip of his presidency. Late on Tuesday, Jordan cancelled a summit in Amman where Biden had been due to hold talks with King Abdullah, and the Egyptian president, Abdel Fatah al-Sisi, after the US president’s visit to Israel. Jordan’s foreign minister, Ayman Safadi told Al Jazeera the summit was cancelled because “there is no use in talking now about anything except stopping the war”. The White House later issued a statement, saying: “After consulting with King Abdullah II of Jordan and in light of the days of mourning announced by President Abbas of the Palestinian Authority, President Biden will postpone his travel to Jordan and the planned meeting with these two leaders and President Sisi of Egypt.” Palestinian president Mahmoud Abbas had earlier pulled out of meeting, after declaring three days of national mourning. In a statement, Abbas said: “What is taking place is genocide. We call on the international community to intervene immediately to stop this massacre. Silence is no longer acceptable.” Protests broke out across the West Bank after the hospital blast, and in Ramallah, the seat of the Palestinian Authority, demonstrators threw rocks at the Palestinian security forces who fired on the crowds with stun grenades. Biden was still scheduled to hold talks with the Israeli prime minister, Benjamin Netanyahu, seeking to show US solidarity with Israel in the wake of the 7 October Hamas attack which killed more than 1,300 Israelis, in the hope of deterring intervention from the Iran-backed Hezbollah militia from across the border with Lebanon. At the same time, the US president was hoping to rein in Israeli retribution against Gaza and its 2.3 million population, who are under constant bombardment while running out of water, food and medical supplies. The UN says more than 3,000 Palestinians have died in the 10 days since the Hamas attack. As a condition of Biden’s visit, Israel agreed to a humanitarian package which included corridors into Gaza for relief supplies and safe areas for Palestinian civilians. But on the eve of his arrival, the border with Egypt, where aid has been stockpiled, remained closed. Gaza City is in northern Gaza, which Israel ordered to be evacuated of civilians ahead of a planned ground offensive, but many Palestinian residents refused to leave their homes or were unable to travel, including the patients at the al-Ahli hospital. It was packed with Gazans wounded by earlier airstrikes and those seeking shelter from the bombardment. Over the past two days, the Israeli air force has also struck urban areas in Khan Younis and Rafah, both of which are in the south of the enclave, where Gazans were told to seek shelter. The border crossing at Rafah, through which aid convoys are waiting to enter, was among the targets. The UN Relief and Works Agency, UNWRA, reported an airstrike on Tuesday on one of its schools in central Gaza, where families displaced from the north had sought refuge. Six people were reported to have been killed. The UNWRA commissioner-general, Philippe Lazzarini, called the bombing at the al-Maghazi refugee camp “outrageous” and warned the death toll was likely to rise. “It again shows a flagrant disregard for the lives of civilians. No place is safe in Gaza any more, not even UNWRA facilities,” Lazzarini added. Even before the blast at the Gaza hospital, the visit was a gamble for Biden in terms of his international reputation and his domestic standing before an election year. The US believed it had struck humanitarian agreements with Netanyahu’s government over the past two days but these did not come to fruition. The president’s trip was announced by the US secretary of state, Antony Blinken, after more than seven hours of talks with Netanyahu and his national security cabinet. The Washington Post and Haaretz reported that the announcement was held back until the Israeli leadership agreed corridors for humanitarian aid to enter Gaza and the creation of safe areas for civilians that would not be bombed. Blinken said Biden was coming “at a critical moment for Israel, for the region and for the world”. He said Israel would brief Biden on its war aims and strategy, and on how it would conduct operations “in a way that minimises civilian casualties and enables humanitarian assistance to flow to civilians in Gaza in a way that does not benefit Hamas”. Rishi Sunak is understood to be considering a visit to Israel, with sources saying it could be as early as this week. However, plans are still being drawn up and could change as a result of the situation on the ground, including the bombing of a hospital in Gaza. Convoys of lorries carrying emergency food water and medical supplies are waiting on the Egyptian side of the border with Gaza waiting for the crossing point at Rafah to open, while Palestinians with foreign citizenship wait on the other side to leave the enclave. Egypt controls the border but requires Israeli agreement on what and who is allowed to pass through it. By Tuesday evening, the gate had still not been opened, but the border post and nearby urban areas were hit by airstrikes. At least 49 Palestinians were killed in Israeli strikes that hit homes in Rafah and Khan Younis, Gaza’s interior ministry said. The UN human rights office denounced the “appalling reports” of civilians being killed in southern Gaza where they had been told to flee for their own safety by the Israeli authorities. The office’s spokesperson, Ravina Shamdasani, appealed to Israel to avoid “indiscriminate or disproportionate attacks”. Asked about airstrikes on Rafah, an Israeli military spokesperson, Lt Col Richard Hecht, said on Tuesday: “When we see a target, when we see something moving that is Hamas, we take care of it. It’s as simple as that.” Israel has partly restored water supply to southern Gaza but the UN said it constituted only 4% of the normal flow into the territory. The lack of clean water and the presence of bodies under the rubble has brought fears of an epidemic. Hospitals are in a state of collapse in the absence of electricity and fuel for generators. “We are overwhelmed. We’re running out of supplies. We have got to get supplies into the Gaza Strip. Time is of the essence here. The clock is ticking,” UNRWA spokesperson Juliette Touma told the BBC. Israel has amassed a large force around Gaza’s borders in preparation for a potential invasion, in the wake of the Hamas attack on 7 October. The extremist group is holding hostage 199 Israelis, including women and children, inside Gaza. Standing alongside the German chancellor, Olaf Scholz, on Tuesday, Netanyahu compared Hamas to the Nazis. “The savagery that we witnessed perpetrated by the Hamas murderers coming out of Gaza were the worst crimes committed against Jews since the Holocaust,” he said. The Israeli ground assault has been held back during Blinken’s diplomatic initiative and amid fears that it could trigger an offensive by Hezbollah on Israel’s northern border. Briefing reporters on Tuesday, Hecht suggested a ground assault was not an inevitability. “We are preparing for the next stages of war,” he said. “We haven’t said what it will be. Everyone is talking about a ground offensive but maybe it will be something different.” The UN human rights office said on Tuesday that Israel’s order to evacuate northern Gaza could constitute the forcible transfer of civilians, which is a crime under international humanitarian law. The UN has said more than a million people have been forced from their homes. “We are concerned that this order, combined with the imposition of a complete siege of Gaza, may not be considered as lawful temporary evacuation and would therefore amount to a forcible transfer of civilians in breach of international law,” the UN’s Shamdasani said. In his talks with Israeli and Arab leaders this week, Biden will also be seeking to ward off a wider regional conflagration after threats from Hezbollah and its backer, Iran. Israel has ordered the evacuation of 28 villages to create a 2km security zone on its Lebanese border, as Netanyahu warned Israelis they should prepare for a long battle. “And I have a message for Iran and Hezbollah: don’t test us in the north. Don’t make the same mistake you once made. Because today the price you will pay will be much heavier,” the prime minister told the Knesset on Monday. The US has deployed two aircraft carrier groups to the region and about 2,000 US troops had been put on alert for non-combat roles in possible support of Israel. The White House has asked Congress to approve more than $2bn (£1.6bn) in additional assistance for both Israel and Ukraine.