A man has been arrested on suspicion of a terrorism offence in connection with the Manchester Arena attack.
Twenty-two people were killed when Salman Abedi detonated a bomb at the end of a concert on 22 May 2017.
A 24-year-old man, from Manchester, is being held on suspicion of engaging in the preparation of acts of terrorism or assisting others in acts of preparation.
He was arrested at Manchester Airport after arriving back in the UK.
Greater Manchester Police said the man, from Fallowfield, remained in custody for questioning.
Det Ch Supt Simon Barraclough said the force remained “committed to establishing the truth surrounding the circumstances of the terror attack”.
“Over four years have passed since the atrocity took place but we are unwavering in our dedication to follow each line of inquiry available so that we can provide all those affected by the events at the arena with the answers they rightly deserve,” he added.
Hundreds of people were also injured when Abedi, who died in the bombing, detonated his device in the arena foyer at the end of an Ariana Grande concert.
His younger brother Hashem Abedi was jailed for at least 55 years in August last year after being found guilty of murdering the 22 victims.
He was also convicted of attempted murder – encompassing the injured people – and conspiring to cause explosions.
The brothers spent months ordering, stockpiling and transporting the deadly materials required for the attack.
A public inquiry into the attack started in September last year to explore the circumstances leading up to and surrounding the bombing.
This includes whether the attack could have been prevented, what happened on 22 May 2017, the security arrangements around the arena, the emergency response to the bombing and the radicalisation of Salman Abedi.