First Minister Carwyn Jones said his thoughts are with all those affected by the London mosque terror attack.
He described it as "another senseless attack".
My thoughts are with those affected by the terrible incident at #FinsburyPark – another senseless attack on innocent people.
Plaid Cymru leader Leanne Wood also tweeted her thoughts.
Looks like there's been another terrorist attack in London. My thoughts are with all affected.
Police say a 47-year-old man has been arrested in connection with the incident. They said there were no other suspects.
One man has died and ten people were injured in the attack.
Detectives have been given more time to question a man from Cardiff arrested in connection with the Finsbury Park attack.
South Wales Police has arrested a man after abusive comments about the Finsbury Park attack were made on social media.
Officers visited a van - believed to be the one used in the London attack the next day - in the early hours of Sunday, ITV News has learned.