The Israeli military said Monday that an initial investigation into the killing of 15 emergency workers in south Gaza last month showed that the incident occurred “due to a sense of threat.”

It said it had identified six Hamas militants as being in the vicinity during the incident in the city of Rafah.

In a statement, the military said it was conducting a more in depth investigation but the preliminary “inquiry indicated that the troops opened fire due to a perceived threat following a previous encounter in the area”, and that six of the individuals killed “were identified as Hamas” militants.

The emergency workers were shot dead on March 23 and buried in shallow graves. The Israeli military initially said it opened fire after unmarked vehicles approached in the dark, but changed its account after video emerged showing clearly marked ambulances and fire trucks with their lights on coming under fire.

deeper investigation would be conducted in the coming days and its findings would be presented to the public, the Israeli military said.

The Red Crescent Society did not immediately respond to a request for comment on the Israeli findings.

After the incident, the Palestine Red Crescent Society called for an independent international investigation and said “that the targeting of its ambulance convoy” was “a full-fledged war crime, reflecting a dangerous pattern of repeated violation of international humanitarian law.”

The emergency workers were from the Red Cross, Red Crescent, U.N. and the Palestinian Civil Emergency Service.