U.S. intelligence officials are less certain which Palestinian group may have fired the rocket, saying they have “low confidence” that it was launched by Palestine Islamic Jihad.

U.S. spy agencies believe that the blast at a Gaza hospital a week ago was caused by a Palestinian rocket that suffered engine failure and broke apart into two pieces, with the warhead striking the hospital’s parking lot, intelligence officials said Tuesday.

Speaking to reporters by phone, the intelligence officials said they had “high confidence” in their assessment that it was not Israel that fired the rocket, but they were less certain which Palestinian militants fired the projectile on the evening of Oct. 17.

“We assess with high confidence that Israel was not responsible for the explosion at the hospital and that Palestinian militants were responsible,” an intelligence official said. “We assess with low confidence that Palestine Islamic Jihad was responsible for launching the rocket that landed on the hospital.”