The younger brother of the Manchester bomber, Salman Abedi, will be extradited to Britain before the end of the year, according to the Libyan prime minister.

Hashem Abedi, 20, was arrested in Libya shortly after his older brother blew himself up at the Manchester Arena on 22 May last year, killing 22 people.

In an interview with the BBC in Italy, Fayez al-Sarraj said Libya was working with British authorities.

The prime minister said: “I think from here to the end of this year we will finish all the legal procedure in Libya. We are fully cooperating because we understand the suffering of the families of the victims of this terrorist attack. We as Libyans also suffer in Libya from attacks. So the subject is important for us. According to the general prosecutor we can extradite. After we complete the legal process in Libya, it is only a matter of time.”

Greater Manchester police (GMP) said counter-terrorism officers had been granted a warrant for Hashem’s arrest and that the Libyan authorities were asked earlier this year to consider extraditing him to the UK.

They believe they have enough evidence to charge him with the murder of 22 people, the attempted murder of others who were injured, and conspiracy to cause an explosion.

Sarraj added: “We are not delaying, but this is a legal process. Sometimes it takes a long time, even in other countries. So the case needs time, and as a country we are following up and working with the British embassy.”

Detectives know the two brothers travelled together to Libya from the UK in April last year, with Hashem remaining in Libya, the country of their parents’ birth. At the end of April, Salman, 22, returned to Manchester to carry out the atrocity at the end of an Ariana Grande concert, buying the components in local stores and assembling his bomb in a rented city centre flat.

Both brothers were born in Manchester and went to school in the city.

Hashem is being held by a militia group in Libya, which has been ravaged by civil war. A photograph of him was released inside the Tripoli-based Special Deterrence Force anti-terrorism unit after his detention on 24 May.

No request has been made to extradite the brothers’ father, who was reportedly arrested shortly after Hashem. Ramadan Abedi was being interviewed by a TV crew in Tripoli when he was taken by masked gunmen, witnesses said in May.

If Hashem returns to the UK, he will be taken into custody on arrival and is likely to be charged immediately.

A spokesperson for Greater Manchester police said: “We are still awaiting the outcome of the CPS request for Hashem Abedi’s extradition from Libya.

“The extradition proceedings are in progress and we are grateful to the Libyan authorities for considering our extradition request. As proceedings are ongoing, it is essential that we respect the Libyan legal process and therefore we cannot provide any further detail at this time.”