At least four people were killed and 17 more were wounded in a terror attack in the Austrian capital Vienna, authorities said on Tuesday.

Austria's Interior Minister Karl Nehammer said the main assailant, who was killed by the police last night, was a sympathizer of the ISIS terror group.

The 20-year-old was known to police as he was arrested last year for attempting to travel to Syria to join the ISIS terror group, Nehammer told Austrian news agency APA.

He also said that at least one other suspect was still on the run, urging citizens to stay indoors and keep away from public places.

Local media identified the terrorist as Kujtim F., who had both North Macedonian and Austrian citizenship.

He was released from jail in December, due to his young age.

Die Presse daily reported that the authorities confirmed four people died and 17 others were wounded in the terror attack.

A 28-year old police officer was among those seriously injured in the attack.