HRW’s Lebanon researcher Ramzi Kaiss told The Guardian: “Israel’s assurances that it is using US weapons lawfully are not credible. As Israel’s conduct in Gaza and Lebanon continues to violate international law, the Biden administration should immediately suspend arms sales to Israel.

The airstrike on the ambulance center in Al-Habariyeh came without warning before 1 a.m. on March 27. No fighting had been reported in the area.

The victims had been at the center for the night shift, and were named as twin brothers Hussein and Ahmad Al-Shaar, aged 18; Abdulrahman Al-Shaar, 19; Mohammad Hamoud, 21; Mohammad Al-Farouk Aatwi, 23; Abdullah Aatwi, 24; and Baraa Abu Kaiss, 24.

Samer Hardan, head of the local Civil Defense center who was among the first responders, told The Guardian: “We examined every centimetre looking for parts of bodies and their possessions. We saw nothing military-related. We knew (the victims) personally, so we could identify their remains.”

The Guardian examined the remnants of a 500lb Israeli MPR bomb and a US-manufactured Joint Direction Attack Munition (JDAM) recovered by first responders from the scene of the attack. Pictures of the shrapnel sent by the Guardian were further verified by Human Rights Watch and an independent arms expert.

JDAMs are guidance kits produced by US aerospace company Boeing which attach to 500-2,000lb “dumb bombs” and convert them into GPS-guided precision missiles. They have been key to Israel’s war effort in Gaza and Lebanon, and have been one of the most requested munitions from the US.

Josh Paul, a non-resident fellow with Democracy for the Arab World Now and a former State Department employee, said: “The State Department has approved several of these (weapons) transfers on a 48-hour turnaround. There is no policy concern on any munitions to Israel other than white phosphorus and cluster bombs.”

Human rights experts say attack was violation of international law, and that US supplying of weapon defies 1997 Leahy law.

Kassem Al-Shaar, father of Ahmad and Hussein, said he had warned his sons not to volunteer.

My sons wanted to do humanitarian work, and look what happened to them. Israel wouldn’t dare to do what they did if it wasn’t for the US standing behind them.”