Police hunting the network behind Manchester suicide bomber Salman Abedi said they made "significant" arrests and seized items they believe are "very important" in raids linked to the investigation.
Security services found bomb-making materials during a number of raids following the attack at the Manchester Arena.
One suspect device was blown up in a controller explosion and security sources previously said there is a possibility other materials are yet to be found.
They also arrested eight men have been arrested during the raids in Manchester, Wigan and Nuneaton. However, A woman arrested in the Blackley area of Manchester was released without charge.
"I want to reassure people that the arrests that we have made are significant," said Greater Manchester Chief Constable Ian Hopkins. "Initial searches of premises have revealed items that we believe are very important to the investigation."
The arrests followed the detainment of Abedi's father, Ramadan Abedi, in the Libyan capital of Tripoli. In interviews Mr Abedi had maintained his son was innocent.
His youngest son, Hashem Abedi, was also arrested in Tripoli, while, British police picked up Ismail Abedi, the bomber's older brother, in Chorlton, south Manchester.
Mr Hopkins also hit out at the leaks of intelligence by US agencies, saying they had caused "distress and upset" to the families of victims of the atrocity.
Forensic photographs of sophisticated bomb parts and information published by The New York Times had caused "much distress for families that are already suffering terribly with their loss", he said.
The force has reportedly stopped sharing intelligence relating to the attack with the US government after concerns that American intelligence officers were continuing to leak confidential details of the investigation to the American media.
Theresa May said she would tell US President Donald Trump that intelligence shared with the US "must remain secure" in a sign of the UK authorities' anger at the repeated leaks of sensitive information to the media.
Intelligence agencies believe a terrorist network was established to carry out the attack.
A source close to MI5 told Reuters Abedi had been on its radar. They said at any one time there could be 3,000 subjects of interests to MI5 and Abedi was part of "a large pool" classed in that category.
"Abedi was one of a larger pool of former subjects of interest whose risk remained subject to review by MI5 and its partners," he said. "Where former subjects of interest show sufficient risk of re-engaging in terrorism, MI5 can consider re-opening the investigation, but this process inevitably relies on difficult professional judgements based on partial information."
Since 2013, British security services have thwarted 18 militant plots in the UK, including five following an attack in central London in March, the source added.
