A sixth person was arrested in the UK on Wednesday evening over Monday's bombing at Manchester Arena, the BBC reported.
Police said they had arrested a woman after an armed raid at a block of flats in Blackley, north Manchester.
A fifth arrest earlier on Wednesday in Wigan, involved a man who was carrying a package that is now being "assessed", police said.
An eyewitness told the BBC the man had been held by "undercover armed police".
He said workers in his office had been told to stay inside and lock their windows, and that a red package had been "moved to a clear part of the street".
Suicide bomber Salman Abedi killed 22 people and injured 64 outside an Ariana Grande pop concert in Monday night's bombing.
Earlier on Wednesday, the bomber's father, Ramadan, and younger brother, Hashem, were arrested in Libya.
Hashem, 20, was reportedly arrested in the capital Tripoli on suspicion of links with the Islamic State (ISIS) group, according to Reuters.
The UK raised its terror threat level to the highest level of "critical" on Tuesday night, meaning more attacks may be imminent.
Meanwhile, military personnel are being deployed to protect key sites after the UK's terror threat level was raised.
Before news of the Tripoli arrests emerged, Greater Manchester Chief Constable Ian Hopkins said on Wednesday, "I think it's very clear that this is a network that we are investigating.”
"And as I've said, it continues at a pace. There's extensive investigations going on and activity taking place across Greater Manchester, as we speak," he added.