Hundreds of Palestinians were killed in an explosion at a Gaza City hospital on Tuesday, according to officials in the Hamas-controlled territory.

The Gaza Health Ministry said at least 500 people died, and blamed an Israeli airstrike. Israel’s army said the hospital was hit in a failed missile attack by militants from the Islamic Jihad group.

The Israeli military said that the hospital had been hit in an attempted missile strike by the Gaza-based militant group Islamic Jihad. Prime Minister Benjamin Netanyahu also said Israeli planes didn’t attack the hospital and blamed Islamic Jihad.

Turkey and Egypt were among countries to condemn the attack and blame Israel for it. The Pentagon said it didn’t immediately have information about who was responsible.

Israel has been bombing Gaza and preparing its forces for a potential ground invasion as it seeks to crush Hamas, which is considered a terrorist organization by the US and European Union.

Global leaders are stepping up diplomatic efforts to prevent an escalation in the war, amid fear that Iran and other Hamas allies may be drawn in, and also to enable humanitarian aid to reach Gaza. US President Joe Biden is due to depart for the region later on Tuesday. His proposed summit in Jordan with the leaders of that country plus Egypt and the Palestinian Authority has been canceled after the hospital blast, according to a White House official.

The Anglican-run Al-Ahli Arab Hospital was housing thousands of displaced Palestinians who fled the Israeli bombing in east Gaza City. Hamas said it fired a long-range rocket toward Israel’s north in response to the hospital attack.

Read more: Brutality of Surprise Attack Unites Israel Around One Goal: Crush Hamas

Mahmoud Abbas, president of the Palestinian Authority which controls the West Bank — the largest Palestinian territory — declared three days of mourning after the hospital blast. Abbas left Amman, where he was due to meet on Wednesday with Biden and the leaders of Egypt and Jordan, and returned to the West Bank according to the official PA news service. Hundreds of Palestinians in Jenin took to the streets in protest.

Egypt’s Foreign Ministry condemned what it said was an Israeli airstrike on the hospital as a violation of international law. It also called on Israel to stop airstrikes near the border crossing between Gaza and Egypt, where thousands of Palestinians have fled to escape bombing further north in the territory. Turkish President Recep Tayyip Erdogan also condemned Israel.

The US doesn’t have “all the facts” about what happened at the Gaza hospital where officials in the Hamas-controlled territory say hundreds were killed by an Israeli airstrike, said Pentagon Deputy Spokeswoman Sabrina Singh.

The Israeli military has said that in past conflicts, about one in every five rockets launched by Gaza militants misfires and lands within their own territory.

Before the hospital blast, Gaza officials had cited a confirmed death toll of about 2,800 Palestinians during 10 days of Israeli bombardment. The Oct. 7 attack in Israel by Hamas killed more than 1,400 Israelis.

--With assistance from Zaid Sabah and Marissa Newman.

(Updates with Biden summit in Jordan canceled in sixth paragraph.)