Britain’s MI5 investigates how it missed warnings about Manchester bomber, Salman Abedi

British domestic security service MI5 has launched two urgent inquiries into how it missed the danger posed by Manchester bomber Salman Abedi amid claims his interest in being a potential terrorist killer was repeatedly reported to the authorities.

One review began last week to quickly identify any glaring errors, while the other will be more in-depth, sources said.

On Sunday, the home secretary, Amber Rudd, refused to comment on whether opportunities were missed to spot the murderous intent of the 22-year-old before last week’s deadly attack, as national security became the major issue in the general election campaign.

The reviews come with security officials warning that the threat from Islamist terrorism keeps rising and is at an “unprecedented scale”, with other attack plots feared.

Investigators believe Abedi, whose parents come from Libya, may have received terrorist training in the country, where some areas are believed to be a safe haven for jihadis. He returned to the UK from Libya just days before exploding a homemade bomb packed with metal bolts and screws and carried in a rucksack, murdering 22 people after the Ariana Grande concert at Manchester Arena on May 22.

Teachers and religious figures in Manchester who knew Abedi raised concerns about his extremist views on multiple occasions and over several years.