The newspaper quoted British members of parliament in a report published on May 13, according to which 400 ISIS fighters have returned to Britain from Middle Eastern countries.

Members of the Joint Parliamentary Committee on Human Rights noted that hundreds of ISIS members have not been brought to justice despite their involvement in what they called “murder, terrorist attacks and persecution of minorities in Iraq and Syria.”

The committee called on the British government to take steps to ensure that they can be tried in British courts, and not in Iraq or Syria, where the “crimes” took place.

“This is something that the UK cannot simply ignore just because it is happening overseas,” said Lord David Elton, chairman of the Joint Committee on Human Rights.

He added, “We know that British citizens have committed the most horrific crimes in Iraq and Syria under the ISIS regime, and we have a duty to bring them to justice.”

Elton noted that no ISIS fighter had been “successfully” prosecuted for international crimes in the UK, and he believed this was “unacceptable.”

Elton called for further action by the UK government to identify the perpetrators, some of whom may have returned to the UK, while others are likely being held in camps in Syria.

The committee's report also called for greater transparency about how the government uses its power to strip Britons of their citizenship because of their links to the organization.

Britain has stripped the citizenship of a civilian, Shamima Begum, who lives in a camp in northeastern Syria, because of her affiliation with the Islamic State.