An unclassified U.S. intelligence report, seen by Reuters on Thursday, estimated the death toll from a blast at a Gaza hospital was "probably at the low end of the 100 to 300 spectrum," but added that the assessment may evolve.

Palestinian officials said 471 people were killed in the blast at Al-Ahli al-Arabi Hospital late on Tuesday. Gaza's health ministry blamed an Israeli air strike, while Israel said the blast was caused by a failed rocket launch by militants.

"We judge that Israel was not responsible," said the unclassified U.S. intelligence report. "Our assessment is based on available reporting, including intelligence, missile activity, and open-source video and images of the incident.

"We estimate the number of deaths is probably at the low end of the 100-to-300 spectrum. 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 report said "only light structural damage at the hospital" has been observed and there was "no observable damage to the main hospital building and no impact craters."

Israel has responded to an Oct. 7 rampage by Hamas gunmen who killed 1,400 Israelis by vowing to destroy the group, putting the 2.3 million people living in Gaza under a total siege, and bombarding the enclave in strikes that have killed thousands and made more than a million homeless. Israel is also preparing a ground offensive.