The security minister, Ben Wallace, has said he would not put officials’ lives at risk to rescue UK citizens who went to Syria and Iraq to join Islamic State, insisting “actions have consequences”.

“I’m not putting at risk British people’s lives to go looking for terrorists or former terrorists in a failed state,” he told BBC Radio 4’s Today programme.

He was speaking on Thursday after it was revealed Shamima Begum, one of three pupils from Bethnal Green, east London, who left to join Isis four years ago, told the Times she wanted to return to the UK. Speaking from a refugee camp in north-east Syria, Begum, who is nine months pregnant with her third child, told the newspaper: “All I want to do is come home to Britain.”

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Her other two children have died from illness and malnutrition, with Begum saying she believed the third would be “taken care of – health-wise at least – in the UK”.

Wallace said that as a British citizen, Begum had a right to return home, but anyone who joined Isis should expect to be investigated, interviewed and “at the very least prosecuted” on their return.

There are currently no British diplomats in Syria because of security risks. If Begum wanted to return to the UK, she would have “to make her way to Turkey or Iraq to consular services there”, he added.

Questioned on whether the fact that Begum was 15 when she ran away might generate sympathy from the Home Office, Wallace said: “People know what they’re getting into.

“This is a terrorist group, one of the worst ever in the world, that butchers people and has been responsible for the deaths of dozens of British citizens.”

One of the other two schoolgirls from Bethnal Green academy who flew from Gatwick to Istanbul on 17 February 2015, Kadiza Sultana, is reported to have died in an airstrike on Raqqa, the former capital of Isis’s territory.

All three had married foreign Isis fighters. Begum, who said she did not regret her decision and seeing a severed head in a bin “didn’t faze me at all”, married a Dutch Muslim convert 10 days after her arrival in Syria.

Two days ago, a new counter-terrorism act, which will raise the maximum penalty for some terrorism offences to 15 years’ imprisonment, was given royal assent.

Sir Peter Fahy, a former chief constable of Greater Manchester police, told Today: “The biggest challenge if she did come back will be how the police will keep her safe and how she wouldn’t be some sort of lightning rod for both Islamic and far-right extremists.

“If she still holds those views, that’s clearly going to be an enormous challenge and you can understand why the government is not particularly interested in facilitating her return.”

Commenting on the wider issue of foreign fighters a Whitehall source said: “There are no easy answers. You do not just have foreign fighters – you have foreign fighters’ relatives, widows, spouses and of course children, and children who may not have any connection with British citizens.

“How are those children protected and looked after? It has not yet been fully worked through. This is all quite fresh and people are still working through what is the best thing to do.

“We cannot declare they are stateless, but we also said if they can be tried effectively where they are, that is good. There is no requirement for a British citizen to return to the UK if they can face justice where they are and the crimes were committed [there].

“That does not apply of course to non-combatants. We have got to make sure that if they do return to Britain, and it has not been possible to prove they were involved in fighting, they may be ideologically damaged by this. That is going to take some resource. We are trying to rehabilitate people – adults will be in a different position to children because we will not have other reasons to detain people, so they are not a threat to themselves or other people.”

Theresa May’s official spokesman said: “Anyone who has travelled to Syria for whatever reason has put themselves in considerable danger but also potentially poses a very serious national security risk to the UK.

“Any British citizen who does return from taking part in the conflict must be in no doubt they will be questioned investigated and potentially prosecuted. Decisions on how people are dealt with are made on a case by case basis to ensure the most appropriate action is taken. Whatever the circumstances of an individual case we have to and we will protect the public.”

Rushanara Ali, the Labour MP for Bethnal Green and Bow, said: “At the time, when Shamima Begum and two other girls disappeared and it was feared they were heading for Syria via Turkey, I made representations to the then home secretary, Theresa May, and the head of counter-terrorism at the Metropolitan police.

“I appealed to them to work with the Turkish authorities to prevent the girls from crossing the border into Syria. Unfortunately, despite the efforts of the UK authorities, the girls did get into Syria and, as subsequent reports suggest, they joined IS [Isis].

“If it is the case that Shamima Begum is trying to return to the UK, it is now a matter for the UK police, security services and the Foreign Office, who will rightly need to consider public safety and our national security in cases such as these.”