A man was being held in custody Sunday after three people were stabbed at a London Underground train station in an attack police were treating as a "terrorist incident"

A man was being held in custody Sunday after three people were stabbed at a London Underground train station in an attack police were treating as a "terrorist incident".

One witness shouted "You're no Muslim" at the suspect as he was pinned down by officers at a suburban police station, amateur video footage showed, while a pool of blood was seen in the ticket hall.

Sky News reported that witnesses had said the lone suspect spoke of Syria and had "apparently shouted 'this is for Syria'," although it did not quote anyone.

Police could not confirm the report when contacted by Agence France Presse and it is not evident from video footage circulating online.

Saturday's attack came at the end of a week in which the British parliament voted to extend air strikes on ISIL from Iraq into Syria.