UK police arrest 19-year-old over Manchester attack

British police arrested a 19-year-old man on Sunday in connection with the Manchester suicide bombing that killed 22 people.

The arrest was made during a raid in the Gorton area of Manchester on "suspicion of offences contrary to the terrorism act," the Greater Manchester police said in a statement on Twitter.

Police said earlier on Sunday they were also searching an address in Rusholme area. Thirteen men are now in custody after a man and a woman were released without charge.

Members of Manchester suicide bomber Salman Abedi's network are still potentially at large, British interior minister Amber Rudd said on Sunday, after the terrorism threat level was lowered because of significant progress in the investigation.

Prime Minister Theresa May said earlier that developments in the investigation meant that intelligence experts had decided to lower the threat level from its highest rating "critical," meaning an attack could be imminent, to "severe".

Rudd, asked during an interview on BBC television whether some of the group were still at large, said: "Potentially. It is an ongoing operation. There are 11 people in custody, the operation is still really at full tilt in a way."

Greater Manchester Police said later on Sunday that they had arrested the 19-year-old man and a 25-year-old man earlier on suspicion of terrorism offences.

When asked how many potential militants the government was worried about, Rudd said the security services were looking at 500 different potential plots, involving 3,000 people as a "top list," with a further 20,000 beneath that.

"That is all different layers, different tiers. It might be just a question mark about one of them or something serious with that top list," she said.

The government has previously complained that technology companies were not doing enough to tackle the use of their networks both to promote extremist ideology and for communication between militant suspects via encrypted messages.

Rudd said Britain was making good progress with internet companies on this but that more could be done. Technology companies such as WhatsApp say they cannot break end-to-end encryption.

"I believe we can get them to be more successful in working with us to find a way of getting some of that information," she said.

"The area that I am most concerned about is the internet companies who are continuing to publish the hate publications, the hate material that is contributing to radicalising people in this country."