Salman Abedi, the man suspected of blowing himself up among a crowd exiting an Ariana Grande concert in Manchester on Monday, wasn't a refugee. But his parents were, and that makes Mr. Abedi the latest name on an extremely worrying list of second-generation citizens to violently turn against the countries and the societies their parents worked so hard to join.

The attack on Manchester Arena – which killed 22 people, including young children, and left dozens more with severe injuries – was claimed by the Islamic State group. The extremist group didn't name Mr. Abedi, but referred to the concert bomber as "one of the soldiers of the Caliphate."

Security experts say second-generation citizens, because of their feeling of cultural dislocation, are particularly vulnerable to the brand of propaganda produced by IS – and may be being specifically targeted by the jihadi organization as potential recruits.

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Read more: 'Pure terror': Young concert-goers tell of chaos in moments after Manchester blast

Read more: Explosion at Ariana Grande concert: What we know so far about the Manchester attack

Opinion: The Manchester attack will change British life for the worse

The concert attack was the deadliest in Britain since 2005, when 52 people were killed by bombs on London's bus and subway systems. It was also the second attack on Britain this year, following a truck-and-knife assault on pedestrians and police in March that killed four people in London's Westminster district.

In the wake of the Manchester attack, British Prime Minister Theresa May raised the country's "terror threat level" from severe to critical, meaning "not only that an attack remains highly likely but a further attack may be imminent." Mark Rowley, the head of the national counterterrorism police, indicated that soldiers are being deployed into the streets of British cities alongside police for the duration of the alert.

The 22-year-old Mr. Abedi was identified Tuesday by Manchester police as the suspected bomber. British media reported that he was born in Manchester to parents who fled the violent repression of Moammar Gadhafi's Libya.

Little else is known about Mr. Abedi – British authorities have been tight-lipped about the investigation and only released Mr. Abedi's name after it was leaked by U.S. officials – but his profile as the child of Muslim immigrants is similar to that of other recent Islamic State and al-Qaeda devotees who have brought terror to the cities of Europe.

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Second-generation citizens born in France to parents who had immigrated from Algeria carried out the Charlie Hebdo massacre in the centre of Paris in 2015. The Belgian-born children of Moroccan immigrants masterminded the shooting and bomb attacks on the Bataclan nightclub and Stade de France later the same year. All five perpetrators of last year's bombings of the Brussels airport and subway had a similar profile.

"If the story of radicalization and Islamism in Europe is about anything, it's about second-generation immigrants, children of immigrants who feel culturally dislocated … a sense of dislocation related to being brought up in Western culture and finding something doesn't quite fit," said Shashank Joshi, a senior fellow at the London-based Royal United Services Institute for Defence and Security Studies.

That dislocation, Mr. Joshi said, creates an opening that Islamic State propagandists – who produce videos featuring Muslims killed in Syria and Iraq by Western bombs – are skilled at exploiting, turning angry youths into soldiers willing to strike those they live among.

It's not yet clear how Mr. Abedi felt about his life in Manchester, a city with high youth unemployment and a fast-growing Muslim population. British media reported Mr. Abedi had been a student at the city's Salford University, where he studied business and management before dropping out two or three years ago.

He last lived in a red-brick walk-up in the middle-class district of Fallowfield, in the south of Manchester. Heavily armed police surrounded the home Tuesday morning and blew the white door off its hinges before storming inside with assault rifles raised. At least one other south Manchester property was raided and a 23-year-old man, reportedly Mr. Abedi's older brother, was taken into custody.

Mr. Abedi lived just a short walk from a girls' high school that gained infamy three years ago when two students – twin sisters Salma and Zahra Halane – left their homes and moved to Islamic State-controlled Syria after being radicalized online.

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Police said they were still investigating whether Mr. Abedi acted alone, or whether he was part of a network.

The claim of responsibility from IS will be closely examined, as will the material used in making the bomb that Mr. Abedi detonated to such deadly effect.

Security experts saw worrying signs that the bombing represented a step up in terms of Islamic State's ability to carry out attacks in Europe.

While 130 people died in the November, 2015, attacks on the Paris nightlife, most of those who were killed were hit by gunfire. A trio of suicide bombers who simultaneously targeted soccer spectators at the Stade de France killed one passerby in addition to themselves.

The SUV-and-knife assault on Westminster in March, meanwhile, was decidedly low-tech.

The high death toll in Manchester, however, suggests the concert bomb was built by someone who knew what they were doing.

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"What scares me is that the person who did this was in possession of a very effective explosive, unlike what happened in Paris in November, 2015," said François Heisbourg, chairman of the London-based International Institute for Strategic Studies. "This guy either received an extremely effective explosive, or cooked it up himself – in which case he was very lucky. My fear is that it's the former, and the bomb-maker is still at large."

While IS has a history of only claiming attacks that it had a direct or indirect hand in, it wasn't clear whether Mr. Abedi had any direct contact with the self-declared caliphate, or whether he was merely inspired by the jihadi group. A U.S. government official told Reuters that investigators were looking into whether Mr. Abedi had recently travelled to Libya, and whether he had any contact with Islamic State militants there.

The IS claim of responsibility – posted on a social-media channel it regularly uses to make announcements – matched poorly with events on the ground in Manchester. The statement referred to multiple explosive devices, when Manchester police found only one bomb, and the IS claim conspicuously made no mention of the fact the group's "soldier" had died in the attack.

The Manchester bombing comes at a time when IS is facing the likelihood of defeat on the ground in Iraq and Syria.

The group has lost more than 60 per cent of the territory it once controlled in Iraq, including most of Mosul, the city from where leader Abu Bakr al-Baghdadi proclaimed his caliphate in June, 2014. All but two neighbourhoods of Mosul are now under the control of the Iraqi army, which has been accused of carrying out torture and extrajudicial executions in the recaptured neighbourhoods.

IS is rapidly losing ground in Syria too, with air strikes by the U.S.-led coalition clearing the way for an advance by Kurdish fighters toward the city of Raqqa, the de facto IS capital, and the city that has lived longest under its horrific interpretation of Islamic sharia law.

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Western policy-makers will now have to consider whether the Manchester attack – if it was indeed carried out by IS – represents a violent death throe, or a signal that the group will carry on its campaign of terror even if it loses its territorial base in Iraq and Syria.

"If anything, this sort of attack could become more, not less, common" as IS suffers military defeats in Syria and Iraq, said Andrew Gawthorpe, a lecturer on security studies at Leiden University in the Netherlands who has also taught British military officers at London's Joint Services Command and Staff College. "There's a chance we're seeing a bid for relevance in this attack, as they lose territory."