The east London schoolgirl who left the UK to join Islamic State has compared the Manchester Arena bombing to airstrikes by the western allies that killed non-combatants in Isis-held areas.

Shamima Begum, 19, says she wants to return to Britain and is asking for “forgiveness”, having given birth to a son on Saturday while in a refugee camp in Syria.

A debate has broken out about whether Begum, who travelled to Syria in 2015 aged 15, should be allowed to return to Britain having joined Isis, which has claimed responsibility for terrorist attacks on the UK.

The Manchester Arena attack in May 2017 killed 22 people after a suicide bomber detonated a device packed with shrapnel at the end of a pop concert.

In the latest of a series of interviews she has given while in the camp, Begum told the BBC she had regrets about the Manchester attack: “I do feel that is wrong. Innocent people did get killed,” she said.

“It’s one thing to kill a soldier, it’s fine, it’s self-defence. But to kill people like women and children, just like the women and children in Baghuz who are being killed right now unjustly by the bombings. It’s a two-way thing really.”

Begum continued: “This is kind of retaliation. Their justification was that it was retaliation so I thought that is a fair justification.”

“That was unfair on them … They weren’t fighting anyone. They weren’t causing any harm. But neither was I and neither [were the] other women who are being killed right now back in Baghuz.”

Begum’s departure to Syria was seen as a propaganda triumph for Isis, but Begum has said she had not wanted to become a poster girl for the group: “I didn’t want to be on the news at first. I did hear a lot of people were encouraged to come after, but I wasn’t the one who put myself on the news. We didn’t want to be on the news.”

Amid the debate about whether she should be allowed to return to Britain, it has been asked whether legally she can be stripped of her British citizenship.

The home secretary has suggested rewriting the 650-year-old law of treason to make it easier to prosecute returning jihadists.

Sajid Javid told the Daily Telegraph it was “worth looking at carefully” whether the ancient law could be updated to be used against British extremists. Javid has previously said he would do everything in his power to prevent those who “hate Britain” from returning to the UK.

Begum took full responsibility for her decision to leave Britain, saying she alone was “the one who made the choice”. She added: “Even though I was only 15 years old, I could make my own decisions. But I will admit, it’s my fault right now. I just want forgiveness from the UK. Everything I’ve been through, I didn’t expect I would go through that.”

She said while in Britain she had been lured by Isis propaganda videos about the “good life they can provide”. She had also viewed beheading videos and those glorifying Isis fighters.

The father of her newborn son is an Isis fighter and despite her four years with the sworn enemies of the UK, Begum said: “I actually do support some British values.”

Begum also said in the latest interview that if she made it back to Britain and was charged and convicted, she wanted her family to look after her son.

Her discovery in a camp last week has highlighted the issue of what western countries should do about their citizens who are now fleeing areas formerly controlled by Isis that have been retaken by its enemies.

Downing Street has rejected Donald Trump’s call for Britain to take back extremists who have fought with Isis. Trump urged European countries, including the UK, to repatriate 800 captured Isis fighters to their home countries and put them on trial. He said that if they did not the US and its allies would be forced to release them.

Responding to his calls, a No 10 spokesman said: “Foreign fighters should be brought to justice in accordance with due legal process in the most appropriate jurisdiction. Where possible, this should be in the region where the crimes had been committed. We continue to work closely with our international partners on this. The government will do all it can to ensure the safety and security of the UK.”

Trump’s comments were echoed by a representative of Kurdish-led authorities in north Syria where about 800 foreign fighters are being held in prisons, along with about 700 women and 1,500 children in camps for displaced people. Abdulkarim Omar, co-chair of foreign relations in the Kurdish-led region, said they would not free foreign Isis detainees but countries must take responsibility for them. He described the detainees as a “timebomb”, saying fighters could escape if the Kurdish-led autonomous area was attacked.

The UK’s lead commissioner for counter extremism, Sara Khan, said more was needed to understand the tactics of extremist groups and how they targeted young people such as Begum. She said one challenge was that a lot of extremist content online was seen as lawful. “Shamima was remorseless in her supporting of Daesh [Isis],” she said.

She added: “I see lots of legal, extremist, radical content online. There is a legitimate question of freedom of speech – we must protect freedom of expression in this country – but I want to see more challenging of extremist beliefs and extremist ideology. We all have a role in that regard. Schools can play an important role in having those conversations … Faith leaders have a role in deconstructing Islamist ideology and beliefs.”

Speaking on BBC Radio 4’s Today programme, Khan said she was concerned about what had radicalised the 19-year-old and what lessons could be learned about what attracted her to extremist ideas.

“It’s important to understand when she travelled … she was aware of Daesh beheadings and executions … was becoming more religiously inclined. There are questions about how a young girl was exposed to extremist ideology – some online – and what more we can do to counter than ideology.

“What support can we give to families fearing their children are being targeted by Islamist extremists?”