Two properties are being searched in Manchester and Chester in connection with the suicide attack following an Ariana Grande Concert.
The Manchester property being searched is in the Whalley Range area of the city.
Police gave no further details on the search of the Chester home.
No arrests have been made and the searches are ongoing.
News of the searches come after a 23-year-old man was arrested in the early hours of Monday morning in Shoreham-by-Sea, West Sussex, in connection with the attack.
New CCTV of the Manchester bomber Salman Abedi has been released by police.
The younger brother of the Manchester bomber has said Salman Abedi was radicalised online in Britain.