Syrian Kurds have said they will hold trials for Islamic State fighters from more than 50 countries, including about 30 from Britain, after becoming exasperated by a failure to reach international agreements over what to do with them.

The Kurdish-dominated administration in north-east Syria said it is holding 1,000 male fighters in overcrowded detention centres and a further 4,000 Isis women in refugee camps, many of whom are accused of involvement in the terror group’s crimes.

Local authorities had hoped to strike agreements with western and other governments to either repatriate fighters and other accused people to face justice in their home country or to set up an internationally recognised tribunal.

But there has been no meaningful progress since Isis lost the last of its territory nearly a year ago. On Thursday, the Syrian Kurdish external affairs ministry unilaterally declared it would start putting people on trial.

Fener al-Kait, assistant minister in the external affairs ministry, said: “This is an international crisis and an international solution must be found. Unfortunately, many states have not responded to our appeals.”

Unlike in neighbouring Iraq, the Syrian Kurdish administration said it will not levy the death penalty on former Isis fighters. Those found guilty of war crimes will be sentenced to life imprisonment. Frontline fighters could receive sentences of up to 20 years, although this would mean expensive detention in a region recovering from Syria’s bitter civil war.

Britain has refused to repatriate adults from Syria and stripped the UK citizenship of anybody it considers a dual national. This includes Shamima Begum, who left east London to join Isis as a teenager and remains in a refugee camp in the country.

Begum has appealed against citizenship deprivation and a ruling on her case is due on Friday. She fled the UK aged 15 to live under Isis with two friends, and subsequently bore three children, all of whom have since died.

Other Britons or former Britons held in prisons in the region are believed to include Shahan Choudhury, who left London in 2014. He said he had acted as a gravedigger during Isis’s last phase, burying victims of the conflict.

Another is Hamza Parvez, a former police cadet from London, who joined Isis in 2014 and appeared in online propaganda videos urging other Britons to travel and join up, in the early phases of the self-styled caliphate.

Syria’s Kurdish forces were instrumental in helping remove Isis from Syria. Its military provided the ground forces that eliminated the group’s hold on the territory in March last year but have been unable to turn that into a strong diplomatic or security position.

They suffered a significant setback when the US president, Donald Trump, allowed Turkey to invade the border region in northern Syria in October. Ankara then set up a security zone in which Syrian Kurdish forces were excluded.

Conditions in the prisons, where there are a handful of guards and little space for prisoners, are cramped and insanitary. There are fears they could become breeding grounds for future extremism.

The Syria Kurds hope that if they start putting foreign fighters on trial, some western governments will provide extra money to secure their detention, although this has not been forthcoming in the past.

The Foreign Office said that anyone who has fought for, or supported Isis, should face justice “in the most appropriate jurisdiction, which will often be in the region where their offences have been committed”.

A spokesperson said they could not comment specifically on the Syrian Kurds announcement but added: “Any internationally supported justice mechanism must respect human rights and the rule of law as well as ensure fair trials and due process.”