The BBC has learned that the UN has repeatedly ignored requests from bereaved families for information to help the official investigation into the Beirut port explosion which killed 219 people in August last year.

The probe has been beset by delays, rows and recriminations, leaving families and survivors no closer to finding out who, if anyone, was to blame, as BBC Middle East correspondent Anna Foster reports.

When Ariana Papazian describes her mother Delia's death she does it clearly and calmly. She remembers every detail. The sound, and the silence that followed. The way she touched her mum's hair, and the exact words she used as she desperately tried to wake her up.

Ariana was just 16 on the day of the blast, and she wants answers about why she lost her beloved parent.

"I feel like my mother doesn't have a value, my mother's life doesn't have a value. My own health doesn't have a value. Like we are not humans."

The official investigation into the devastating explosion was supposed to provide the truth. But it has stalled. It's been suspended several times because senior political figures who were called to give evidence made complaints. A protest against the lead judge Tarek Bitar led to violent clashes in which seven people died.

The dispute has split Lebanon's cabinet, which hasn't met for a month now in a country that desperately needs leadership if it's to escape its current crises.

That lack of progress has led to international criticism. But a vital organisation that could have helped has ignored requests - the United Nations.

One week after the explosion it called for "a prompt and independent investigation that leads to justice and accountability". But the BBC has learned that when bereaved families asked for information to help that very inquiry, the UN didn't reply.

The Beirut Bar Association represents nearly 2,000 families and survivors at the investigation. Its chairman sent three separate letters directly to UN Secretary General Antonio Guterres, asking for some specific details.

They requested two things. Firstly, all available satellite photos taken on the day of the blast by member states. And secondly, whether Unifil (United Nations Interim Force in Lebanon) checked the MV Rhosus - the ship that carried the explosive material which caused the explosion - back in 2013, before it arrived at Beirut port.

Aya Majzoub, Lebanon Researcher with Human Rights Watch, explained why the satellite images are vital.

"Until this day we don't know what caused the explosion, we don't know if it was an intentional act, we don't know if it was caused by negligence, we have no idea," she says.

"And so satellite imagery of the port on that day would be very important in trying to answer outstanding questions about why the explosion happened."

Last week Russia said its space agency Roscosmos was preparing to hand over images of the blast site, after a request from the Lebanese president, Michel Aoun.

The first of the families' letters was sent by the Bar Association on 26 October 2020. A follow-up was dispatched three weeks later on 19 November, noting "it has been more than 100 days since the blast, to date none of the member states or Unifil has sent any photos or information".

The third letter, dated 17 March 2021, states: "Seven months have passed since the blast and five months since our letter, and unfortunately our letters remain unanswered and unacknowledged. Lebanon is a founder member of the UN and is asking for help."

Ramzi Haykal, a veteran lawyer in Lebanon and a member of the Beirut Bar Association, is defiant.

"Let me tell you something, we are fighters" he said. "We are fighters by law. And we will continue fighting, because we are responsible for 1,800 people who asked us to represent them to obtain justice."

Aya Majzoub thinks the UN response has fallen short. "I'm sure the secretary general is inundated with letters and requests, but it's been disappointing to see the lack of co-operation with the Lebanese authorities. Also the lack of an international investigation into the blast, there's much more the international community could be doing that they aren't."

I asked the UN about these letters, and why none of the three had even been acknowledged. The secretary general's office told me the UN is committed to supporting the Lebanese people, and has mobilised to help the victims. But it didn't explain why those specific letters - so important to the investigation and the quest for the truth - had simply been ignored, only saying it focused on answering those from officials.

The survivors and bereaved families say they deserve better, and that one of the biggest explosions in history should be properly investigated.

But while the Lebanese authorities procrastinate, and other countries don't give help where they can, the answers that a nation desperately needs will remain elusive.