Joe Biden on Wednesday delivered full US backing for Israel in person, on a solidarity visit in which he blamed Islamist militants for a deadly rocket strike on a Gaza hospital and announced the resumption of urgent aid to the besieged Palestinian enclave.

The US president's whistlestop trip came just hours after Tuesday night's blast at the Ahli Arab hospital in the Gaza Strip, sparking fury in Arab countries which blame Israel and protests in Muslim countries from Egypt to Pakistan.

Lebanon's Iran-backed Hezbollah movement called for a "day of rage", after its ally Hamas, which runs the Gaza Strip, said 471 people were killed in the blast on the hospital compound, where many displaced by Israeli bombing were sheltering.

But European intelligence agencies cast doubt on the death toll. One told AFP: "There wasn't 200 or even 500 deaths, more likely between 10 and 50."

The official also backed Biden and the Israelis' account, who said the strike at the Christian-run hospital was from a malfunctioning Palestinian rocket.

In Tel Aviv, Biden said he was "deeply saddened and outraged" by the blast, but added: "Based on what I've seen, it appears as though it was done by the other team, not you."

Israel, Washington's long-standing key Middle East ally, has blamed the armed Islamic Jihad movement which like Hamas is proscribed as a terrorist group by the United States and other Western governments.

"Based on the information we have seen today it (the blast) appears the result of an errant rocket fired by a terrorist group in Gaza," Biden told a news conference later.

Biden has defended Israel's right to defend itself, and understood the "all-consuming rage" to hit back at those responsible for the October 7 attacks, which saw Hamas fighters shoot, mutilate or burn to death some 1,400 people.

But he added: "I caution this while you feel that rage: don't be consumed by it. After 9/11, we were enraged in the United States. While we sought justice we also made mistakes," he said.

Israel said afterwards it had agreed to Biden's request to allow aid into the besieged Gaza Strip via Egypt after mounting concern about dwindling supplies and warnings of a humanitarian catastrophe.

But it said it was limited to "food, water and medicine" and conditional on it not being used by Hamas, added Prime Minister Benjamin Netanyahu's office.

Biden also announced plans for "unprecedented" aid for Israel and the Palestinians in Gaza and the West Bank, as part of a wider $100 billion package that includes support for Ukraine.

Moments after Biden took off in Air Force One, rocket alerts were activated in central Israel, east of Tel Aviv. Police said rockets fell near the Lebanese border, causing damage but no casualties.

The horror of the hospital deaths overshadowed Biden's high-stakes regional visit, with Jordan cancelling a summit between King Abdullah II, Biden, Palestinian president Mahmud Abbas and Egyptian President Abdel Fattah al-Sisi.

Israel's military campaign to destroy Hamas, which is holding 199 hostages in the besieged territory, has now claimed the lives of 3,478 people, according to health officials.

Arab countries have almost universally blamed Israel for the hospital strike, either directly or through state media -- including Egypt, Jordan and the United Arab Emirates, which are among the region's few countries which have diplomatic relations with Israel.

The Organisation of Islamic Cooperation -- a 57-member bloc of Muslim-majority countries -- denounced Israel's backers for granting the country "impunity" in its war with Gaza. (AFP)