The United Nations has launched an investigation into an unidentified strike on a U.N. car in Rafah on Monday that killed its first international staff in Gaza since Oct. 7, a spokesperson for the U.N. Secretary General said.

The staffer, a retired Indian Army officer named Waibhav Anil Kale, was working with the U.N. Department of Safety and Security and was on route to the European Hospital in Rafah along with a colleague, who was also injured in the attack.

On Wednesday, India's foreign ministry said its diplomatic missions were "in touch with relevant authorities" on the investigation, and helping to bring home the remains.

Israel has been moving deeper into Rafah in southern Gaza, where more than a million people had sought shelter, and its forces pounded the enclave's north on Tuesday in some of the fiercest attacks in months.

Israel's international allies and aid groups have repeatedly warned against a ground incursion into Rafah, where many Palestinians fled, and Israel says four Hamas battalions are holed up. Israel says it must root out the remaining fighters.

In a statement on Monday after Kale's death, U.N. Secretary General Antonio Guterres reiterated an "urgent appeal for an immediate humanitarian ceasefire and for the release of all hostages," saying the conflict in Gaza was continuing to take a heavy toll "not only on civilians, but also on humanitarian workers".

Palestinian health authorities say Israel's ground and air campaign in Gaza since Oct. 7 has killed more than 35,000 people and driven most of the enclave's 2.3 million people from their homes.

On Tuesday, the U.N. Secretary General's deputy spokesperson, Farhan Haq, said the U.N. had set up a fact-finding panel to determine the responsibility for the attack.

"It’s very early in the investigation, and details of the incident are still being verified with the Israeli Defence Force," he said.

There are 71 international U.N. staff members in Gaza currently, he said.

Israel, which launched its Gaza operation after an attack on Oct. 7 by Hamas-led gunmen who killed some 1,200 people and took more than 250 hostages, according to its tallies, has ordered civilians to evacuate parts of Rafah.

The main United Nations aid agency in Gaza, UNRWA estimates some 450,000 people have fled the city since May 6. More than a million civilians had sought refuge there.