The Manchester Arena suicide bombing occurred partly because of poor UK security cooperation with Libyan authorities, security officials from the North African state claim.
Salman Abedi, 22, detonated a homemade device at an Ariana Grande concert in Manchester in May, which killed 22 and wounded scores more.
Abedi, who also died in the blast, was of Libyan origin. He and his father Ramadan were known to have ties with the Libyan Islamic Fighting Group (LIFG), which is linked to Al-Qaeda.
Senior Libyan security officials have blamed the lapse in security on a lack of UK intelligence sharing.
They claim to enjoy closer cooperation with the CIA than the UK security services.
They told the BBC that Abedi was under close observation during his trip to Libya just a month before the devastating attack, and that they had gained information about his network of contacts in the UK.
A serving general from the UN-mandated Tripoli government said they were keen to improve information sharing as quickly as possible.
A spokesman for the Special Deterrence Force said the attack had been plotted as long ago as December 2016.
Abedi’s father and his brother Hashem are currently in custody, but it is not known if information has been gained through coercion.
Libyan authorities say parts used to assemble the bomb, which the British police are now saying Abedi built alone, were sourced in the UK by both Hashem and Salman Abedi.
They then left the country. Salman Abedi returned to carry out the operation in Manchester, where he lived in close proximity with a number of Libyan exiles linked to the LIFG.