Experts have warned that the IDF may have violated international law by the means it used to infiltrate the hospital during a raid on Tuesday, CNN reports.

During the raid, Israeli special forces, dressed as civilians and medical staff infiltrated the Ibn Sina hospital in the occupied West Bank city of Jenin and killed three Palestinian men, both Israeli and Palestinian officials said. Israel said one of the men was a Hamas fighter, while the other two brothers who were killed were linked to Islamic Jihad.

“The Israeli forces involved in the operation were dressed in civilian clothing and at least some were dressed as medical personnel, who enjoy protection under the law of armed conflict,” Aurel Sari, a law professor at the University of Exeter in the UK, told CNN.

As part of a single attack it “violates the prohibition of resort to perfidy,” he added.