A total of 10 people are in detention in Britain and Libya over Monday's suicide bombing on a pop concert in the northwestern English city of Manchester by a British-born man of Libyan origin.
A teenage boy and a woman arrested by British police this week have since been released without charge, leaving eight in custody on UK soil who were arrested "on suspicion of offences contrary to the terrorism act".
In Libya, killer Salman Abedi's father and brother are in detention.
Abedi reportedly returned from Libya only a few days before the attack which killed 22 people, including several children, but police are still trying to pin down his movements as well as determine whether he was part of a wider network.
Here are the details of the arrests so far:
Tuesday, May 23:- Masked police arrest a 24-year-old man in the Chorlton area of south Manchester near where Abedi is believed to have lived. Police had earlier given the man's age as 23.
An eyewitness told AFP that police shouted at the man to lie on the ground before taking him away. British media indicated that this man is highly likely to be Abedi's older brother Ismael.
The brother was described in media reports as "outgoing" compared to Salman, who was "very quiet."
Wednesday, May 24:- Police arrest three more men in south Manchester aged 18, 21 and 24, a short walk from the house where Abedi lived.
Omar Alfaqhuri, a neighbour who lives just in front of a house that was raided, said he saw "a massive deployment of police forces" during the arrest in the night and a man he named as "Adel" taken away.
"They blocked the whole street," he said, adding that he saw the man handcuffed and taken away in a car.
He said his neighbours were a "nice quiet family".
An 18-year-old man, who police said was carrying a suspect package, is arrested in Wigan, a town near Manchester. No further details were given about him.
Another man, 22, is arrested in the town of Nuneaton in central England, widening the British police probe beyond areas in and around Manchester.
Libya's Deterrence Force, which acts as the police of the Tripoli-based Government of National Accord, arrests Abedi's father Ramadan, saying it had already arrested his brother Hashem on Tuesday.
A spokesman said the brother was aware of Abedi's attack plan and both belonged to the Islamic State group, which claimed responsibility for the attack.
Abedi's father reportedly protested his son's innocence in the hours before his arrest.
In Manchester, a 34-year-old woman is arrested in an apartment block in Blackley, an area north of the city centre by armed police. She is later released without charge.
Thursday, May 25:- A 16-year-old boy is arrested in Withington, a suburb of south Manchester. The boy is later released without charge.
A 38-year-old man is arrested in Blackley.
Friday, May 26- A 30-year-old man is arrested in Moss Side, an area of Manchester which has been associated with social deprivation and gangs.