The Palestine Red Crescent Society said on Sunday that a medic who had been missing since an Israeli attack on ambulances in Gaza last month is currently being held by Israeli authorities.

"We have been informed by the International Committee of the Red Cross that medic Asaad al-Nsasrah is being held by the Israeli occupation authorities," the PRCS said in a statement.

"His fate had remained unknown since he was targeted along with other PRCS medics in Rafah," it said, referring to the attack that left 15 medics and rescuers dead.

When contacted for comment on the PRCS's latest announcement, the Israeli military referred AFP to an earlier statement noting that army chief Lieutenant General Eyal Zamir had ordered a thorough investigation into the attack.

The killings occurred in the southern Gaza Strip in the early hours of March 23, days into a renewed Israeli offensive in the Hamas-ruled territory. 

They have since sparked international condemnation, with Israel insisting there were militants in the ambulances.

The PRCS has charged that Israeli soldiers gunned down the team with bullets to their upper body with "intent to kill".

Eight staff members from the Red Crescent, six from the Gaza civil defence agency and one employee of the UN agency for Palestinian refugees were killed in the attack, according to the UN humanitarian office OCHA and Palestinian rescuers.

Their bodies were found buried near the site of the shooting in the Tal al-Sultan area of Rafah city, in what OCHA described as a mass grave.

The team was ambushed while responding to distress calls from Palestinians in an area near Rafah that had been struck by an Israeli air strike, the PRCS had said.