The gunman accused of killing 51 people in New Zealand has handwritten a letter from jail expressing his political and social views, prompting Prime Minister Jacinda Ardern to say that should never have been allowed, media said on Wednesday.

The New Zealand Herald had an image of the six-page letter and envelope from the alleged mosque shooter, Brenton Tarrant, sent from Auckland Prison, which was posted online on the controversial image board 4chan.

It was said to have been in response to a letter sent to him by a person named Alan who is said to live in Russia.

Read more: Reuters