Islamic State (Isis) is using the digital currency bitcoin as part of its fundraising efforts, according to a cybersecurity expert.

Ido Wulkan, a senior web-intelligence analyst at the Singapore-based firm S2T, claims to have concrete evidence linking an Isis cell based in the United States to bitcoin fundraising on the dark web.

"Due to the increasing efforts of social media websites to close Isis-related accounts it was estimated that global jihad activists would seek refuge in the dark web," Wulkan told the Israeli newspaper Haaretz.

As part of an "international jihad project", Wulkan came across an Isis fundraising site, linked through a closed Turkish forum.

The unnamed site contained the following message from a user by the name of Abu-Mustafa: "Many of us live within the United States, and some are prominent with the community on both coasts.

"We are currently working with recent reverts to Islam and generally training brothers to struggle to establish a new Islamic front both in the US and around the world."

Abu-Mustafa goes on to explain how only bitcoin donations are approved by the cell, confirming previous suspicions that Isis is using the cryptocurrency in order to avoid detection by western governments.

A pro-Isis blog last year laid out the reasons why the terrorist organisation needed to use alternative financing methods, however Wulkan believes he has found the first proof that this is actually taking place.

"There was smoke, and now we have found the fire," Wulkan said, revealing that a bitcoin address associated with Abu-Mustafa's group had already received around five bitcoins ($1,150, £760) through fundraising.

The account has reportedly since been shut down by the FBI, however a counter-extremist think tank has claimed attempts to police dark web activity is futile.

"Motivated extremists and terrorist affiliates can evade such measures easily through the dark net and virtual private networks," the report from Quilliam Foundation stated last month.

"[Shuttering extremist activity] risks driving fanatics on to the dark web where they are even harder to track."