The Army has launched an investigation after far-right activist Tommy Robinson posted a picture online surrounded by soldiers.
The former English Defence League (EDL) leader, whose real name is Stephen Yaxley-Lennon, posted an image online posing with soldiers.
He also shared a video with a crowd of army personnel who were cheering his name.
"A moment like this makes it all worth while. Today I met real British heroes (SIC)," he wrote in the Facebook post.
The Army said it is aware of the photograph and footage and is "investigating the circumstances surrounding this".
A spokeswoman said: "Far right ideology is completely at odds with the values and ethos of the Armed Forces. The Armed Forces have robust measures in place to ensure those exhibiting extremist views are neither tolerated nor permitted to serve."
Imam Asim Hafiz, Islamic religious adviser to the Armed Forces, said that "any form of racism, discrimination or extremism is taken extremely seriously and will be dealt with accordingly".
He added: "The Armed Forces remain absolutely committed to welcoming individuals from across all faiths and cultures into its ranks."
The Muslim Council of Britain said Mr Robinson "does not represent our Armed Forces, however much he tries to claim otherwise".
A spokesman added: "He will rile against the very real steps taken to make the military more diverse. He will remain silent on the sacrifices Muslims and others made in the two World Wars. We welcome the swift statement by the Army in disassociating itself from the far-right and we hope that safeguards are put in place to ensure that Islamophobia will have no place in our armed forces."
Agencies contributed to this report
