Police in Great Britain investigating the Manchester Arena bombing have arrested a ninth man while continuing to search addresses associated with the bomber who killed 22 people on Monday, The Associated Press reported Friday.

The name of the man arrested Friday and those of the eight previous detainees have not been released. No one has yet been charged in the bombing, the AP reported.

Britain’s security level has been upgraded to “critical,” which means officials believe another attack may be imminent.

Authorities are seeking possible links between the bomber, Salman Abedi, and militants in Manchester and elsewhere, the AP reported.