Rebels in Ukraine have ousted an international task force of doctors in the country’s wartorn east, denying thousands of civilians urgent medical care.

The self-proclaimed Donetsk People’s Republic has blacklisted Médecins sans Frontières, who said rebel chiefs gave no reason for the ban.

Bart Janssens, MSF’s director of operations, warned that the ruling is likely to lead to the deaths of patients and urged the rebels to reconsider. “As a medical organisation we ethically cannot accept being forced to abandon our patients,” he said.

Medics with the NGO have treated Ukrainian civilians wounded in the war as well as patients with chronic and potentially fatal illnesses including tuberculosis, diabetes and kidney disease. The group supplies more than 75% of insulin in the DPR and almost all its dialysis equipment.

MSF treats around 150 prisoners in the DPR who suffer from drug-resistant tuberculosis. “There is a huge risk that the health of these patients will deteriorate soon,” Janssens said, warning that an interruption to their treatment “will lead to a major risk to public health”.

While a new ceasefire holds, Ukraine’s restive east remains in the grip of a humanitarian crisis, at risk of deteriorating with the onset of winter. The conflict has claimed more than 8,000 lives and injured many thousands more since fighting broke out between government troops and pro-Russian rebels last year. Many doctors and nurses have fled the worst-affected areas and pharmacies are empty.

Since the outbreak of war, MSF has donated medication and equipment to 170 medical facilities across the embattled region and conducted more than 85,000 consultations since March.

The ban is the latest setback for MSF, which has been working in eastern Ukraine since 2011 and working on both sides of the conflict since May 2014.

This month its medical workers watched in horror as patients were burned alive after a botched US airstrike on a hospital in Kunduz, Afghanistan. In September, the organisation was among 10 Western NGOs to be ousted by Ukraine’s rebel-held Luhansk region.

In a statement, a spokesperson for the group said: “MSF has up until now coordinated all its activities with the authorities and is willing to continue this collaboration for the sake of the health of thousands of vulnerable citizens of DPR.”

According to MSF, the organisation received a written notice from Donetsk’s Humanitarian Committee on 19 October asking it to stop its activities and saying its accreditation had been withdrawn. Details of the ban only began to emerge on Friday.

A DPR representative told AFP: “I can confirm the decision to strip accreditation.” The International Committee of the Red Cross and the Czech Republic’s People in Need remain working in the region, according to the rebels. At the time of publication, the rebel’s central media office had not responded to the Guardian’s requests for comment on why the ban was implemented and how authorities will meet the needs of the civilians formerly helped by MSF.