A 17-year-old boy from west London has pleaded guilty to terror offences linked to the neo-Nazi group Sonnenkrieg Division.
Oskar Dunn-Koczorowki admitted two counts of encouraging terrorism.
He entered guilty pleas during an Old Bailey preliminary hearing.
A court order that prevented his identification was lifted by the judge.
He will be sentenced at a later date and will next appear on 25 February.
The charges state that in August this year Dunn-Koczorowki used accounts on the Gab social media site - including one for the Sonnenkrieg Division itself - to post material that would encourage others to prepare or engage in acts of terrorism.
A co-defendant - Michael Szewczuk, 18, from Leeds - also appeared in court, but has not yet entered pleas.
Mr Szewczuk, a Polish national, is charged with five counts of encouraging terrorism and three of disseminating terrorist publications.
A provisional trial date was fixed for 13 May 2019 at Manchester Crown Court.
Both defendants were granted conditional bail.