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 a wider network.
"As it stands, six men and one woman have been arrested in conjunction with the investigation and remain in custody for questioning", the police added.
British police arrested two more people and searched a new site in Manchester suspected of links to the concert bombing that left 22 people dead, as British authorities complained bitterly Thursday about investigation leaks blamed on USA officials.
Eight men have now been detained in Britain connection with Monday's attack.
All the previous arrests in the case were made in and around Manchester in north-west England where the bombing occurred.
Leaks from an investigation into the Manchester terror attack are undermining the probe, British police said today as the BBC reported that police had stopped sharing information with the US. She is later released without charge.More news: Officials back reducing bond holdings this year
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Another brother, 23-year-old Ismail, was arrested on Tuesday in Manchester.
Police and security services are also upset that the name of bomber Salman Abedi was leaked by USA officials and published while police in Britain were withholding the name for what they said were reasons of operational security. His father, Ramadan Abedi, and brother, Hashim, have also been arrested in Libya.
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.
Ahmed Bin Salem, a spokesman for the Special Deterrence Force, also known as Rada, said that Salman's brother Hashem, 20, had travelled from London to Tripoli on April 16.
Such a threat level allows members of the armed forces to replace armed police officers who are responsible for such duties as guarding key sites.
The leaks have opened a diplomatic row as United Kingdom officials are said to be "furious" that their investigation was compromised when photos appearing to show debris from the attack appeared in the "New York Times".