By Francois Murphy

VIENNA (Reuters) - The 23-year-old Syrian refugee believed to have killed a teenager and injured five other people in a weekend stabbing rampage in the Austrian town of Villach became radicalised quickly by using TikTok, officials said on Monday.

The suspect, identified as Ahmad G., had the flag of the Islamic State militant group in his apartment but had not previously attracted Austrian authorities' attention. The case highlights the challenge of preventing so-called lone wolf attacks, when an attacker acts alone without outside help.

His online radicalisation draws further attention to social media platforms like TikTok that can offer users a large amount of content on subjects of interest, which some experts say can accelerate their immersion in them.

"He radicalised himself within three months," a spokesman for prosecutors in the nearby city of Klagenfurt, where the investigation is being handled, told Reuters.

"Not through any other person, personal contact either online or in person. Evidently, he really just consumed videos and decided to commit this act. There was no other person who said 'Do it!'" he said. "He himself confirms it and says he watched videos and then decided he wanted to join IS."

TikTok, in a 2022 post on its website, said it was committed to finding solutions and working with "civil society on combating violent extremism".

The attack came just days after a 24-year-old Afghan drove into a crowd in Munich in neighbouring Germany, killing two people and injuring dozens. Munich lead prosecutor Gabriele Tilmann said there appeared to be an Islamist motivation.

Police said the Villach suspect used a flip knife for the attack and recorded himself swearing allegiance to Islamic State, adding that his aim was to be shot dead by police. Instead, he was arrested within minutes after another Syrian helped to stop him.

A picture of the suspect was widely circulated, showing him sitting in the street appearing to smile as a police officer faced him just moments after the attack.

The suspect is believed to have arrived in Austria in 2019, the prosecutors' office spokesman said, and wanted to travel on to Germany with fake identification so that German authorities would not turn him away as an asylum applicant for having already been in a safe third country, Austria.

A spokesman for Austria's Interior Ministry said the suspect spent four days in custody in Germany in May last year for being unable to pay a fine for falsifying a document, but did not say what kind of document it was.

(Reporting by Francois Murphy; Editing by Dave Graham and Bernadette Baum)