The Army is investigating soldiers for possible links to the English Defence League, the Ministry of Defence has confirmed.
Campaigners say extreme groups have "proactively targeted" the military, with reports of soldiers posing online with EDL material.
In response to a Freedom of Information Act request from The Huffington Post UK, the MoD said it had received reports of "individuals in Army uniform involved with the English Defence League".
It is the first time the government has acknowledged that the reports have been formally investigated by the ministry.
A spokesman confirmed a handful of investigations had been launched in recent years, with two still underway.
One person, who is no longer in the Army, was convicted of affray as a result.
Information for the Royal Navy and the Royal Air Force was unavailable.
The EDL has sought to align itself closely with the Armed Forces, and there have been fears of a "surge in anti-Islamic sentiment" among troops.
In the aftermath of the murder of Lee Rigby in May, the government issued guidance to members of the armed services reminding them not to engage with political groups.
It came after photos emerged, apparently showing serving soldiers posing with EDL propaganda.
Last month Channel 4 News claimed to have spoken to service personnel at an EDL demo, and seen Facebook pages where members of the Armed Forces had 'liked' the far-right outfit.
The MoD told HuffPost UK soldiers were allowed to engage with political groups when out of uniform.
But it added: "Army personnel are expected to abide by the values and standards of the UK Armed Forces at all times and those who are found to fall short of these high standards or to have committed an offence under the Armed Forces Act are dealt with administratively or through the disciplinary process.
"Ultimately, such action may result in dismissal."
It said "fewer than five" service personnel had been investigated in the past four years, of which two were ongoing and one had ended up in the court case.
Ministry of Defence:
I can confirm that we have received reports of individuals in Army uniform involved with the English Defence League (for example posing in photographs), however there is often insufficient detail for us to identify whether or not those involved are in fact Army personnel, and if so who they may be. I can confirm that in the four years up to and including June 2013 fewer than 5 Army personnel were investigated for a disciplinary matter where a connection to the English Defence League is annotated on the record. While some of these investigations remained ongoing as at June 2013,
one resulted in a conviction for affray in a civilian court of a person who is now no longer serving in the Army.
Far-right expert Professor Matthew Goodwin, of Nottingham University, told HuffPost UK: "Particularly since 2001, far-right groups have been more proactively targeting potential supporters within the Armed Forces.
"This is something that state agencies in Germany have been grappling with, and something that I am sure our own armed services are vigorously exploring."
Matthew Collins, of Hope not Hate, added: "It's not endemic, but it's certainly problematic."