(NewsNation) — Israeli military officials say an errant rocket fired by a smaller, more radical militant group called Palestinian Islamic Jihad is responsible for the deadly explosion at a hospital in Gaza.

U.S. intelligence supports that claim.

Here’s what we know about the group authorities believe caused the blast.

Palestinian Islamic Jihad, also known as PIJ, is a Sunni militant group and U.S.-designated terrorist organization committed to the destruction of Israel. Its goal is to create an Islamic state covering present-day Israel, Gaza and the West Bank.

Although it shares the same ideological aims as Hamas, the group is considered even more extreme and doesn’t engage in politics. Instead, it’s focused only on military attacks against Israel.

Historically, those attacks have included suicide bombings, which PIJ has carried out against Israeli civilians and military personnel.

“Palestinian Islamic Jihad only is in the business of terrorism, whereas Hamas is more of a movement. It has proselytizing activities. It has social welfare activities. It has political activities,” Matthew Levitt, Reinhard Counterterrorism Program director at The Washington Institute told NewsNation.

While Hamas and PIJ have had disagreements in the past, Levitt said the two are allies.

With an estimated 1,000 members, PIJ is the second-largest militant group in Gaza and the West Bank after Hamas.

Formed in 1979 as an offshoot of the Muslim Brotherhood in Egypt, the PIJ has amassed an arsenal of rockets, mortars, anti-tank missiles and even drones, according to the CIA’s World Factbook.

The group receives most of its assistance from Iran, which provides military training and weapons, as well as funding.

It also gets help from Syria and Lebanese Hezbollah, which provide safe harbor for leadership and facilitate Iran’s support to PIJ.

If Palestinian Islamic Jihad is responsible for this week’s deadly explosion at a Gaza City hospital, it wouldn’t be the first time the group has killed its own side.

Just last year, PIJ killed 15 Palestinians with errant rockets after firing 1,100 at Israel in response to the death of one of its leaders, according to the National Counterorrism Center.

The group, whose members took part in the Hamas-led attacks on Israel on Oct. 7, has denied that it caused the latest blast.