The UN has been accused of trying to starve out refugees and asylum seekers who are sheltering for safety inside a centre run by the UN refugee agency in the Libyan capital of Tripoli.

One group of about 400 people, who came to the Tripoli gathering and departure facility in October from Abu Salim detention centre in the south of the country, have apparently been without food for weeks.

Among them are 100 minors, according to a recent assessment by the International Organization for Migration. They are “currently starving” apart from some food that other refugees manage to sneak out of another part of the centre, the IOM assessment said. They last received food assistance a “couple of weeks ago”.

Internal documents seen by the Guardian show that the UNHCR is also planning to withdraw food from 600 other refugees and migrants in the centre – who include survivors of bombings, torture, forced labour and other human rights abuses. The majority have already tried to reach Europe by crossing the Mediterranean, but were returned to Libya by the EU-backed Libyan coastguard.

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In a document circulated among UN staff on Tuesday, and seen by the Guardian, the agency said it would “phase out” food catering from 31 December. The document said the information should not be made public before mid-December, when 230 more refugees have been evacuated to other countries, in order to prevent disruption. After that, the facility will no longer be used as a transit centre, the document said, until the remaining refugees and migrants “vacate voluntarily”.

In the document, the UNHCR said that it would continue to finance cleaning in the centre after the withdrawal of food, partly to “prevent the reputational risk of having deficient/broken toilets and showers”. It also said a healthcare clinic on the site would continue to operate.

Facebook Twitter Pinterest Hundreds of migrants who fled a detention centre in coastal Libya crowd around a UN facility in Tripoli. Photograph: AP

An aid worker with knowledge of the situation, who spoke on condition of anonymity, said: “They are starving the population inside the [facility]. They’re just trying to starve them to motivate them to leave. It’s deliberately withholding aid to put people under pressure.”

The group who will be affected by the next food withdrawal include 400 survivors of the 3 July Tajoura detention centre bombing, in which at least 53 refugees and migrants were killed after an airstrike hit the hall in which they were being held. Hundreds of survivors remained on the site of the strike for a week afterwards, staging a hunger strike in protest at the lack of help.

They eventually walked dozens of miles to the gathering and departure facility, where they were let in but told their cases for evacuation wouldn’t be evaluated until they agreed to leave the centre.

One Tajoura survivor told the Guardian this week that if they are forced to leave and fend for themselves in Tripoli “it will be a very dangerous scenario”. Refugees are frightened of forced recruitment by militias, being caught up in the ongoing civil war, or being kidnapped anew by traffickers. Others who have taken a UNHCR offer of money, in return for living alone in Tripoli, say the payments are not enough and they remain in danger. One Eritrean man recently released from Triq al Sikka detention centre was shot last week by men in police uniforms who, he said, were trying to rob him.

“Still now they didn’t give food. I think it is [on] purpose?” an Eritrean refugee in the facility messaged the Guardian this week through WhatsApp. “Everyone is suffering and stressed and we have all decided to stay here until they use force, because being returned to a detention centre means again facing trafficking, torture and abuse.”

The man said he spent more than a year in Abu Salim detention centre, which was repeatedly caught on the frontlines of Tripoli’s ongoing conflict. “[We have] no option until UNHCR gives us a positive response. Even if they leave we will stay here. We have no option, we will not go anywhere. There are no safe places in Libya at this time.”

An 11 November email sent by the Guardian to UNHCR spokespeople, which asked whether denying food to former Abu Salim detainees in the facility was a “deliberate policy on UNHCR’s part”, went unanswered, as did further requests for comment.

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The internal UN document suggest that, after the agency stops using the facility as a transit centre, the property could continue to operate as an “open centre” for refugees and migrants previously held in detention centres, though there are other “possible scenarios”. These include that Libya’s department for combating illegal migration (DCIM) “moves in and forcibly removes all the migrants/asylum-seekers … [to] detention centres”, or that it turns the facility into a detention centre run by its own guards.

The DCIM, which is under the interior ministry of the UN-backed Tripoli Government of National Accord, ostensibly runs a network of migrant detention centres in Libya, though in reality most are run by militias. A litany of human rights abuses, including rape and sexual abuse, labour exploitation and a denial of medical care have been reported.

The UN-run facility opened in December last year to much fanfare. “The opening of this centre, in very difficult circumstances, has the potential to save lives,” said the UN high commissioner for refugees, Filippo Grandi. “It offers immediate protection and safety for vulnerable refugees in need of urgent evacuation, and is an alternative to detention for hundreds of refugees currently trapped in Libya.”