VIENNA:The gunman responsible for an attack in Vienna which left four people dead on Monday night was a convicted supporter of the Islamic State (IS) group who the government says "fooled" official de-radicalisation efforts.

The 20-year-old, named as Kujtim Fejzulai, was shot dead by police and was armed with a shortened Kalashnikov, a handgun, a machete and a fake explosive belt.

According to Interior Minster Karl Nehammer, Fejzulai had dual Macedonian-Austrian nationality and had already been convicted last year of attempting to travel to Syria and trying to join IS.

After that conviction, Fejzulai, whose name suggests he is of ethnic Albanian origin, was sentenced to 22 months in prison, but was released early on parole in December.

"The perpetrator managed to fool the justice system's de-radicalisation programme, to fool the people in it, and to get an early release through this," Nehammer said, suggesting that the attacker had made special efforts to deceive probation officers.

"Therefore there were no warning signs of his radicalisation," he added.

Justice Minister Alma Zadic said that, in line with Austrian law, Fejzulai had been paroled in December 2019 after serving two thirds of his sentence, but also put on three years' probation.

"This enables us to continue to have an influence over the perpetrator beyond the term of their prison sentence," she said, pointing out that this would not have been the case had he simply served his full sentence which normally would have expired in July 2020.

In Fejzulai's case, he was required to report regularly to probation counsellors and the de-radicalisation programme DERAD, "which, according to our current knowledge, he did," Zadic said.

After Monday's shocking attack, Fejzulai's home was raided and the evidence of his radical sympathies became clear.

"It was clear that the attacker, despite all the outward signs of having integrated into society, did exactly the opposite," the minister said.

In a Facebook post, he posed with the Kalashnikov and the machete he would go on to use in the attack together with a caption saying he was "serving the sultanate" and other typical IS messages, Nehammer said.

A statement from the Macedonian interior ministry said he had been born in Moedling, a commuter town to the south of Vienna.

- Born in Austria -

There had been a previous attempt on the part of Vienna authorities to strip Fejzulai of his Austrian citizenship, but this was not successful because "there was not enough evidence about his activities", Nehammer said.

Eighteen further raids have taken place on addresses connected to him, with 14 people detained.

According to police in North Macedonia, a landlocked country in the Western Balkans, around 150 nationals travelled to fight alongside jihadists in Iraq and Syria, mainly between 2012 and 2016.

Most hailed from North Macedonia's ethnic Albanian Muslim minority, who make up around a quarter of the 2.1 million population.

Around half have returned while many others with links to IS have since been imprisoned in jails in North Macedonia or other countries.

The Macedonian interior ministry said they had been asked to provide information on three people with both Austrian and Macedonian citizenship, including Fejzulai.

"The department for international police cooperation in the ministry of internal affairs immediately started to cooperate with the colleagues from Austria and we are intensively cooperating on all elements connected to this case," the ministry said in a written statement.