TEL AVIV, Israel — Palestinian medical officials say they obtained video footage that refutes Israel’s claims about the killing of 15 rescue and aid workers in the southern Gaza Strip last month.

Israel’s military initially said “several vehicles were identified advancing suspiciously toward [Israeli] troops without headlights, or emergency signals” on March 23, and the soldiers opened fire.

But the Palestine Red Crescent Society released a video Saturday it said was found in a cellphone with one of the killed paramedics. It shows clearly marked rescue vehicles with headlights on and red emergency lights flashing. The video was filmed inside one of the vehicles in the convoy.

In the video, there is heavy gunfire over the course of several minutes, and a man’s voice says in Arabic, “Mom, forgive me. This is the path I chose, to help people.”

On Thursday, the Israel military said a high-level military investigation was taking place to determine whether to open a criminal investigation into misconduct over the March 23 incident.

“All claims, including the documentation circulating about the incident, will be thoroughly and deeply examined to understand the sequence of events and the handling of the situation,” the military said Saturday.

After the incident, the crew was missing for more than a week. Rescue teams finally discovered the bodies of 14 Palestinian emergency responders and a United Nations staffer under a mound of sand on March 31.

“One by one they were hit, they were struck. Their bodies were gathered and buried in this mass grave,” Jonathan Whittall, an official with the U.N. Office for the Coordination of Humanitarian Affairs, said in a video at the site where the bodies were found. “They were here to save lives. Instead, they ended up in a mass grave. … It’s an absolute horror what happened here.”

Israel is expanding its military offensive in Gaza after breaking a ceasefire with the Palestinian militant group Hamas last month. In little over two weeks, the Israeli campaign has killed more than 1,300 Palestinians, according to the Health Ministry in Gaza. Israel says it has targeted several Hamas militant and government leaders in the strikes.