Tools of destruction: Images of Manchester Arena bomb equipment leaked

Parts of the bomb used in the Manchester Arena terror attack, including a detonator, battery and shreds of a backpack, have emerged in a series of chilling images.

Manchester suicide bomber Salman Abedi carried his bomb in a Karrimor rucksack triggered with a sophisticated switch held in his left hand, leaked crime scene photographs suggest.

Police found the remains of the bomb’s lightweight metal casing, together with a high quality 12-volt battery and a trigger device containing a small circuit board soldered into one end.

A further four men have now been arrested in police raids following the Ariana Grande concert explosion that killed 22 people and injured at least 119, bringing the total number of arrests to seven.

The evidence discovered in the foyer of the Manchester Arena helps to explain why the security services are so convinced Abedi was part of a wider terrorist cell, as the level of expertise needed to build such a device points to an expert bomb-maker who could still be at large.

Crime scene photographs were leaked to the New York Times, apparently after being shared with US intelligence agencies by British investigators.

The pictures were leaked despite a direct plea from Amber Rudd, the Home Secretary, to the US authorities to stop leaking information about the fast-moving inquiry.

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The official threat level was raised late on Tuesday to its highest level, "critical", meaning an attack is expected imminently.

Police have named British-born Abedi, 22, as the perpetrator of the bombing at the Manchester Arena, which was attended by thousands of children and teenagers.

"It seems likely, possible, that he wasn't doing this on his own," interior minister Amber Rudd told BBC radio.

Rudd also said Abedi had been known to security services before the bombing.

Bomber's father and brother arrested

Salman Abedi's father and younger brother have now also been arrested in Tripoli on suspicion of links with Islamic State.

The force, known as Rada, detained Hashem Abedi, who was born in 1997, on Tuesday evening, spokesman Ahmed Bin Salem told Reuters.

Hashem Abedi had been in touch with attacker Salman Abedi, Bin Salem said, and had travelled from Libya to Britain last month.

"We have evidence that he is involved in Daesh (Islamic State) with his brother. We have been following him for more than one month and a half," Bin Salem said.

"He was in contact with his brother and he knew about the attack."

Salman Abedi, 22, was born in Britain to Libyan parents. Britain's interior minister said earlier that he had recently returned from Libya and had likely not acted alone.

Reuters have reported that his father, Ramadan, was also arrested on Wednesday, quoting a spokesman and a witness.