One of the twin sisters from Manchester who have become brides to ISIS fighters in Syria has updated her Twitter account with what she called "self defence training."

The latest post showed an image of four women in veiled clothing training with their AK-47 assault rifles and handguns at a target off-screen.

The photo was captioned: "Fun day training for self defence in the Islamic State with humble sisters."

However, neither one of the 17-year-old twins Zahra and Salma Halane could be identified because of their clothing.

According to the Daily Mail, the women are reportedly part of the all-female religious police brigade that the ISIS uses to enforce their hard-line interpretation of Sharia law in Raqqa. This police unit also allegedly includes former school girl Aqsa Mahmood.

The twins, who hail from Chorlton, Manchester, left the United Kingdom in June last year. Al Arabiya News said that they flew to Istanbul, and then to Turkey. They were thought to have become brides for fighters in the Islamic State.

Both the twins' husbands have allegedly been killed in action, the Daily Mail said.

The teens' parents told the Daily Mail that the two women are highly intelligent and have a total of 28 GCSE's between the two of them. They were even planning to become doctors and were about to finish their sixth-form college when they became radicalised by Islamic State propaganda in the Internet.

Their parents, Ibrahim and Khadra Jama, attempted to talk the teens out of fighting with the Islamic State during a visit in November. However, both teenagers refused to return to Manchester.

An older brother, Ahmed, is also thought to have joined Al Shabaab in Somalia, where their parents emigrated from.