British women Isis
Dozens of British women are believed to have joined Isis in Iraq and Syria.Twitter

Islamic State (Isis) militants, aided by a British-based intermediary, are offering to pay travel expenses to young and possibly good-looking British teenagers interested in joining the extremist group in Syria as jihadi brides.

Reporters posing as two teenage schoolgirls held regular conversations via social media with a jihadist in the Isis stronghold of Raqqa, northern Syria, for three months.

Upon showing interest in travelling to the self-styled caliphate, the two purported girls, aged 17 and 19, were told they would be given the money to pay for their trip from London to Syria via Turkey.

The sum was to be delivered via cash transfer to a Western Union branch in Sterling, and picked up by an Isis operative in the UK, who in turn was to hand it to the girls.

The investigation by The Times gave an insight into Isis' use of social media and the extent of its worldwide reach to recruit young Muslim women in the West, with the aim of marrying them off to the group's fighters.

Using mainstream social media such as Facebook, Twitter and Ask.fm, as well as instant messaging systems like Wickr and Kik, an Isis militant calling himself Abu Abbas al-Lubnani vetted and groomed the two purported girls over a three-month period, before finalising the money transfer.

'Mujahideen like a good-looking wife'

The jihadist reassured them about the safety of their journey, claiming that thousands of Sunni hardliners travelled to Syria every month without encountering difficulties.

He also asked the girls to provide him with a series of personal details, including a description of their appearance.

"Sorry but I need to know if ur good looking, the colours of your skin," Lubnani told the undercover reporter. "Usually mujahideen don't request a beauty queen, but they like to have a good-looking wife."

He finally agreed to send over cash to Western Union branch without security cameras in London. The girls were to wait near the premises while an Isis middleman picked up the money for them.

"The brother has a wife they can pick up from a certain place that doesn't have a camera then give you the money in their car," al-Lubnani wrote.

The day of the meeting a white man appearing to be Muslim convert showed up at the given location accompanied by a woman in a burka.

"To check this was the correct couple, The Times reporter changed the exact location of the "girls" several times in the space of a few minutes and set out the details in messages to the Lubnani messenger account. Each time the pair moved to the new location," the newspaper wrote.

Realising they were being watched the pair left, the paper said, adding that Counter-terrorism police are aware of the investigation.

An increasing number of women, including dozens of Britons, are believed to have joined Isis in Syria and Iraq over the last 12 months.