(Corrects paragraph 3 to say Israel blamed Islamic Jihad not Hamas)

By Steve Holland

ON BOARD AIR FORCE ONE, Oct 17 (Reuters) - U.S. President Joe Biden will pose "tough questions" in meetings with Israeli leaders during a Middle East trip that has been upended by a strike on a Gaza hospital on Tuesday in which hundreds of Palestinians were killed.

Biden is flying to Israel to meet with Prime Minister Benjamin Netanyahu and show U.S. support in the aftermath of an attack on Israeli villages and military bases by Gaza-based Hamas gunmen that killed hundreds of people on Oct. 7.

After his meetings in Israel, Biden had planned to travel to Jordan for meetings with Arab leaders, but that stop was canceled after the strike on the hospital which Palestinian officials blamed on Israel and Israel blamed on the Palestinian Islamic Jihad group.

Biden will meet with Netanyahu and the Israeli war cabinet and seek a sense of Israel's plans and objectives in the days and weeks ahead, White House spokesperson John Kirby told reporters on Air Force One during the flight to Tel Aviv.

"He'll be asking some tough questions, he'll be asking them as a friend, as a true friend of Israel, but he'll be asking some questions of them," Kirby said.

Israel is expected to launch a ground offensive in Gaza; the United States has been pressing Israelis to allow humanitarian aid in to help civilians.

Kirby declined to specify the nature of the questions Biden intended to ask beyond "what their plans are going forward."

Biden will also meet with Israeli first responders and families of those who lost loved ones in the bloody Hamas assault or whose family members were taken hostage.

Biden will also make public remarks during his visit.

The trip may be overshadowed by the hospital explosion, however.

Gaza authorities say Israel's military was responsible for the bombing; Israeli authorities denied involvement in the strike, which occurred during a massive Israeli bombardment of the enclave in retaliation for the Oct. 7 Hamas attacks.

Biden left Washington earlier on Tuesday on what was supposed to be a complex diplomatic mission, aimed at showing support for long-time U.S. ally Israel, calming the region and shoring up humanitarian efforts for Gaza.

It was unclear what he could accomplish in the wake of the hospital strike, conflicting reports about responsibility, and the cancellation of the summit in Jordan.

"This sort of murky but horrific event makes diplomacy harder and increases escalation risks," said Richard Gowan, U.N. director at International Crisis Group.

"Biden's visit was meant to underline that the U.S. has a grip on the situation. A tragic incident like this shows how hard it is to keep the war in check.”

Biden was originally expected to meet with Israeli Prime Minister Benjamin Netanyahu in Tel Aviv on Wednesday, then fly to Amman to meet Jordan's King Abdullah, Egyptian President Abdel Fattah al-Sisi and Palestinian President Mahmoud Abbas.

Failure to meet with Abbas or any Palestinian official, while meeting Israelis on their soil, may undermine Biden's diplomatic message and draw critics at home and abroad. The U.S. is leaning heavily on Egypt to help with humanitarian efforts.

After the hospital blast, Biden's efforts to date in the Israel-Hamas war were criticized by U.S. Representative Rashida Tlaib, the only Palestinian American in Congress.

"This is what happens when you refuse to facilitate a ceasefire & help de-escalate. Your war and destruction only approach has opened my eyes and many Palestinian Americans and Muslims Americans like me," Tlaib, a Democrat who had previously been muted in her criticism of Biden's policy, said in a post on social media platform X.

More than 70 religious and activist groups, led by the Council on American-Islamic Relations, the largest U.S. Muslim civil rights group, called on Biden to demand a ceasefire in Gaza during his visit. (Reporting by Steve Holland, Michelle Nichols, Matt Spetalnick and Jeff Mason; Editing by Cynthia Osterman and Stephen Coates)