It is unclear what kind of weapon struck the hospital, and both sides blamed each other for the explosion. The Palestinian militant group Hamas, which governs Gaza, said the Israeli military launched an airstrike against the hospital.

The Israel Defense Forces denied responsibility, and asserted that rockets fired toward the Israeli city of Haifa by Islamic Jihad, another Palestinian militant group operating in Gaza, were responsible for the attack.

Reaction to the explosion was swift. Earlier Tuesday, Abbas canceled his scheduled meeting with Biden in Amman, the Jordanian capital, in response to the attack.

Biden condemned the attack in a statement on Tuesday evening, saying that he was “outraged and deeply saddened by the explosion at the Al Ahli Arab hospital in Gaza, and the terrible loss of life that resulted.”

“The United States stands unequivocally for the protection of civilian life during conflict and we mourn the patients, medical staff and other innocents killed or wounded in this tragedy,” Biden said.

The explosion is the latest escalation in the war between Israel and Hamas. In a surprise attack on Oct. 7, Hamas militants stormed out of the Gaza Strip, killing more than 1,200 Israelis and abducting dozens more, while firing rockets at cities including Tel Aviv and Jerusalem. Israel has since hit back by commencing a siege of Gaza and firing its own barrage of retaliatory missiles, killing thousands.

The U.S. has publicly pledged its support for Israel as it seeks to militarily defeat Hamas and end its control over the Gaza Strip. Earlier in the week, Blinken visited Israel and many of its Middle Eastern neighbors in a show of support for Israel and in an effort to get Arab countries to provide support for Palestinians. The Biden administration has transferred munitions to the Israel Defense Forces and has pushed Congress to greenlight new military aid to Israel.

Biden had been expected to meet with Abbas and the leaders of Egypt, Jordan and other neighboring countries in Amman on Wednesday, and then meet with Israeli Prime Minister Benjamin Netanyahu on Thursday. Biden is still expected to meet with Netanyahu this week.