The Manchester Arena bomb attack was planned over several months, since December last year, according to reports.

Salman Abedi had been under surveillance in Libya more than a month before the atrocity which left 22 dead, security officials in the country told the BBC.

Investigators in Tripoli have reportedly highlighted a lack of security co-operation with the UK, and say it has to developed to stop further incidents.

Officials in Libya said that they were watching Abedi from when he arrived in the country, and his father Ramadan and brother Hashem were also under surveillance, it was said.

Salman apparently spent several weeks quietly with his family in Tripoli before returning to Britain and detonating explosives at the Arena on May 22.

On a daily basis Ramadan and Hashem Abedi continue to be interrogated by Libya's Special Deterrence Force, the BBC report.

Special Deterrence Force spokesman Ahmed bin Salem reportedly said the attack was being planned as far back as last December.

He said the force had important information about Abedi's contacts in the UK and Libya.

But Libyan security teams reportedly say they co-operate better with the CIA than they do with London.

According to the report, a senior figure in the UN-backed, Tripoli government wants far closer intelligence sharing to stop any further attacks.

A Libyan security official reportedly claimed that Hashem admitted in detention that back in 2015 he and Salman joined Islamic State.

They added that Hashem bought parts for the bomb while in the UK but left the country at the same time as his brother, who went on to carry out the Manchester attack on his return.