A man has been arrested at Heathrow airport as part of the investigation into last month's deadly suicide bombing in Manchester, British police said on Wednesday.
"The 38-year-old was arrested on suspicion of offences contrary to the Terrorism Act and remains in custody.
"The arrest was planned beforehand and there was no direct threat to the airport," Greater Manchester Police said in a statement.
Police did not immediately confirm when the suspect was detained at Europe's busiest airport, or whether he landed at the airport as part of an extradition procedure.
The arrest comes more than two weeks after the May 22 attack on Manchester Arena at a concert by US pop star Ariana Grande.
The bombing carried out by Salman Abedi killed 22 people, including children, and wounded more than 100 others.
A total of 19 people have been arrested in Britain as part of the terror probe, 12 of whom have been released without charge.
Abedi's father and brother are also in detention in Libya, where authorities say the two brothers were both part of the Islamic State group which claimed responsibility for the deadly attack.
Grande returned to the British city on Sunday evening for a benefit concert for the victims, joined by fellow music stars including Katy Perry and Justin Bieber.
Police in Manchester are still trying to piece together the bomber's final movements and on Tuesday released photos of a bag within which forensics had "uncovered significant evidence".
They also published images of a white car which investigators believe Abedi took items from to build the bomb.
"Although it is positive that we are making significant progress, we still need you to help us build a picture of exactly what led to this atrocity," police said, appealing for anyone who recognised the car or bag to come forward.
The city's police force had previously published CCTV images of Abedi and a blue suitcase he used, in a bid to jog the public's memory of any sightings of the attacker.
The Manchester bombing was Britain's deadliest terror attack in more than a decade.
It prompted the government to raise the country's terror threat level to critical, meaning an attack was expected imminently, but scaled back to severe within a week.
As the probe into the Manchester bombing continued, three men carried out an attack in central London on Saturday evening killing seven people.
The assailants first drove a van into pedestrians on London Bridge, before descending into the nearby Borough Market where they stabbed revellers in the area bustling with bars and restaurants.
A total of 48 people were hospitalised following the attack, which ended when police shot dead the assailants who had been wearing fake suicide vests.
Twelve people arrested since the rampage have since been released without charge, while a 27-year-old man remains in custody.
In Ireland two men were arrested over documentation related to one of the attackers, one of whom has been released without charge.
In the aftermath of the terror attacks the spotlight has fallen on Britain's security services, which admitted to previously having Abedi on their radar and at least one of the London attackers.