LONDON (Reuters) - A decision by Britain to strip a teenage girl of her citizenship after she joined Islamic State in Syria was described as a “stain on the conscience” of the government on Saturday after her three-week old baby died.

Shamima Begum was stripped of her citizenship on security grounds last month, leaving her in a detention camp in Syria where her baby died, the third of the 19-year-old’s infant children to die since she traveled to Syria in 2015.

The opposition Labour party said the move to leave an innocent child in a refugee camp, where infant mortality rates are high, was morally reprehensible. A lawmaker in the ruling Conservative party said it smacked of populism over principle.

“The tragic death of Shamima Begum’s baby, Jarrah, is a stain on the conscience of this government,” Diane Abbott, the opposition home affairs spokeswoman said.

“The Home Secretary (interior minister) failed this British child and he has a lot to answer for.”

Found in a refugee camp in February, an unrepentant Begum sparked a debate in Britain and other European capitals as to whether a teenager with a jihadist fighter’s child should be left in a war zone to fend for herself.

More broadly it has shown the predicament that governments face when weighing the ethical, legal and security ramifications of allowing militants and their families to return.

FILE PHOTO: Renu Begum, sister of teenage British girl Shamima Begum, holds a photo of her sister as she makes an appeal for her to return home at Scotland Yard, in London, Britain February 22, 2015. REUTERS/Laura Lean/Pool/File Photo

Begum left London aged 15 with two other schoolgirls to join Islamic State. She married Yago Riedijk, a Dutch IS fighter who is being held in a Kurdish detention center in northeastern Syria.

After giving interviews to the media in which she said she did not regret traveling to Syria and had not been fazed by the sight of severed heads, she asked to be able to return to London to bring up her baby.

However Home Secretary Sajid Javid withdrew Begum’s citizenship, saying his priority was the safety and security of Britain and the people who lived there.

Polls suggested the move was popular with a majority of Britons but it drew criticism from opposition parties and human rights lawyers, and disquiet among some lawmakers within Prime Minister Theresa May’s party who felt that Britain was exporting its own problems.

Phillip Lee, a former justice minister and member of May’s party, said he had been deeply concerned by the decision.

“Clearly Shamima Begum holds abhorrent views,” he told BBC Radio. “But she was a child. She is a product of our society ... and I think we had a moral responsibility to her and to her baby, Jarrah.

“I was troubled by the decision. It seemed driven by a populism, not by any principle that I recognized.”

Two senior members of the government said on Saturday that the death was a tragedy but that the home secretary took the decision on grounds of national security.

“Any baby dying is an absolute tragedy, and that was a British baby,” the leader of parliament Andrea Leadsom told Reuters. “But nevertheless the home secretary’s core job is to protect the people of the United Kingdom.

“I support his decision.”