Several hundred former marines and others have gathered in Parliament Square in London to support a former Plymouth Royal Marine jailed for killing an Afghan insurgent.
The rally is being held for Alexander Blackman, who is serving life after being convicted of murder. Protestors believe the sentence is unjust.
The MoD has banned military men and women from attending the rally as it has been labelled as a political protest.
An internal review by the Naval service in September 2015 found what Blackman did was "not consistent with the ethos, values and standards of the Royal Marines".