In the guidebook, foreign fighters are instructed to pack "vital belongings" and suitable clothing for the trip, capitalize on their strengths and improve their weaknesses in an effort to "help establish" ISIL. There is also a guide for interaction with Turkish immigration officials.
"It's of interest to the CTIRU [Counter Terrorism Internet Referral Unit] and we have and we will seek its [the ISIL handbook's] removal from websites and social media platforms," a Scotland Yard spokesperson was quoted as saying by the newspaper on Wednesday.
The British authorities' effort to curb the guidebook's easy accessibility online comes amid reports that three London schoolgirls who went missing last week have crossed into IS-held Syria through Turkey.
Additionally, US authorities confirmed British media reports on Thursday that the identity of an ISIL fighter who has appeared in numerous beheading videos was that of UK national Mohammed Emwazi.
Elsewhere, three Central Asian nationals were detained in New York City earlier on Thursday on charges of plotting to join ISIL in Syria, while FBI director James Comey revealed investigations of suspects "in various stages of radicalizing" were being carried out across all 50 US states.
According to the US National Counterterrorism Center's estimates released earlier this month, the militant group in control of large parts of Syrian and Iraqi territories has at least 20,000 fighters in its ranks from around the world.
In the summer of 2014, Turkey banned border crossings for anyone except Syrian citizens, however it was revealed Wednesday that foreigners use fake Syrian documents to pass Turkish border checkpoints.
A number of abductions and killings, in addition to violence toward national and religious minorities, has thrust IS into the spotlight as a violent extremist organization.
