COUNTER-TERRORISM agencies are now almost certain suicide bomber Salman Abedi did not act alone and are investigating a terror “network”.

At least six people in the UK have now been arrested in connection with the attack in Manchester on Monday night that left left 22 dead and more than 60 injured.

One of those detained by police is Ismael, Abedi’s older brother.

In Libya, the bomber’s father, Ramadan, and younger brother, Hashem, have been also been arrested.

Hashem, 20, was reportedly arrested in the capital Tripoli on suspicion of having links with Daesh. Authorities believe he was about to carry out an attack.

Earlier in the day Ramadan had denied Salman was linked to militants or the bombing, saying his family “aren’t the ones who blow up ourselves among innocents”.

He said his son sounded “normal” when he last spoke to him five days ago, adding that Abedi had visited Libya a month-and-a-half ago.

There were reports that members of the public tried to blow the whistle on Abedi several years ago.

An unnamed Muslim community worker told the BBC two people who knew the attacker at college had contacted police after he made statements “supporting terrorism” and expressing the view that “being a suicide bomber was OK”.

US officials reportedly claimed the bomber’s family had warned security services that he was "dangerous".

The 23-year-old’s attack at the Ariana Grande concert on Monday night was the deadliest assault in the UK since the July 7 attacks in London in 2005. He detonated a homemade device packed with nuts and bolts, which exploded in the Manchester Arena’s foyer as thousands of young people were leaving.

On Wednesday afternoon, Greater Manchester Police Chief Constable Ian Hopkins said the level of activity in the investigation was “intense” and continuing “at pace”.

Asked if officers were looking for the person who made the bomb, he said: “I think it’s very clear that this is a network that we are investigating and as I’ve said, it continues at pace, this extensive investigation is going on and activity is taking place across Greater Manchester as we speak.”

Information leaked to the New York Times by US security agencies showed that most of those killed were around the bomber, whose upper torso was “heaved outside the lethal ring toward the Manchester Arena entrance.”

The paper says this is an indicator of a “powerful, high-velocity charge, and of a bomb in which its shrapnel was carefully and evenly packed”, It goes on to say authorities found a Yuasa 12-volt, 2.1 amp lead acid battery at the scene, which will have been used as the detonator. Normally for used powering emergency lighting, this £20 battery is said to be significantly more powerful than batteries often seen in backpack bombs or suicide vests.

The apparent detonator, which British law enforcement officials said was carried in the bomber’s left hand, is also unusual for a manual detonator in a suicide device, in that it appears to have contained a small circuit board soldered inside one end.

The former University of Salford student was born in Manchester to Libyan parents, and travelled to the Middle East frequently. He was involved in gangs and, according to friends, became increasingly religious.

A former classmate of Abedi’s told the BBC that he was a “very jokey lad” but also “very short-tempered” and would get angry at “the littlest thing”.

The man, who did not want to be identified, said Abedi was “away at random times throughout the year”.

He did not know if Abedi was abroad or playing truant because he hung around “the wrong crowd and was very, very gullible”.

The man said that, before leaving the school in 2011, Abedi became “more and more religious” and this might explain why he cut ties with former classmates.

France’s interior minister claimed that the bomber was also believed to have travelled to Syria and claimed he had “proven” links with Islamic State; Gerard Collomb told French television that both British and French intelligence services had information that the attacker had been in Syria.

He added: “We only know what the British investigators have told us. He was a British national of Libyan origin, he grew up in Great Britain.

“All of a sudden he travelled to Libya and then most likely to Syria, became radicalised and decided to commit this attack.”

Though Daesh claimed responsibility for Monday night’s operation, there are few indications the extremist group knew of Abedi or knew that the attack was going ahead.

Prime Minister Theresa May will chair a meeting of the government’s Cobra emergency committee in Whitehall this morning, said Downing Street. The meeting, bringing together senior ministers, officials, police and security agencies, will be the fourth Cobra gathering to deal with the Manchester bombing.