(NewsNation) — U.S. intelligence estimates 100-300 people were killed in the Tuesday bombing of a Gaza hospital that caused worldwide furor, a source familiar with the assessment confirmed to NewsNation.

The estimate was part of an unclassified report sent to Congress Wednesday. Intelligence officials cautioned the information could change as more details become available. 

“We are still assessing the likely casualty figures and our assessment may evolve, but this death toll still reflects a staggering loss of life. The United States takes seriously the deaths of all civilians and is working intensively to address the humanitarian crisis in Gaza,” read the assessment from the Office of the Director of National Intelligence.

President Joe Biden and the White House’s National Security Council previously confirmed U.S. intelligence did not believe Israel was responsible for the bombing of the Gaza hospital.

The report sent to Congress read, “We judge that Israel was not responsible for an explosion that killed hundreds of civilians yesterday [17 October] at the Al Ahli Hospital in the Gaza Strip. Our assessment is based on available reporting, including intelligence, missile activity, and open-source video and images of the incident.”

Militant group Hamas has blamed Israel for the attack, calling it “a crime of genocide,” and other Palestinian groups have also made that assertion. Israeli Prime Minister Benjamin Netanyahu vehemently denied that claim, and the Israeli military released evidence it said proves it was not responsible: aerial footage, photos of the damage and intercepts of militants discussing the attack.

U.S. intelligence also said its current assessment is the group Palestinian Islamic Jihad (PIJ), designated as a terror organization by the U.S., was responsible, as Israel also asserted.

“We continue to work to corroborate whether the explosion resulted from a failed PIJ rocket,” said the report.

Palestinian Islamic Jihad denied responsibility.

“We have made mistakes, I am not going to deny it,” a spokesman for the group told The New York Times. “However, not mistakes of this size.” 

Intelligence officials who briefed members of Congress this week also laid out the evidence that they said showed Israel was not responsible.

“The Senate Intelligence Committee has received and reviewed intelligence related to the attack on Al-Ahli hospital in Gaza. Based on this information, we feel comfortable that the explosion was the (result) of a failed launch by militant terrorists and not the result of an Israeli airstrike,” Senate Intelligence Chairman Mark Warner and Vice Chairman Marco Rubio said in a statement. 

CNN first reported the intelligence report on the attack being sent to Congress.