If confirmed, Friday’s killings in the northern city of Linz – in which an 85-year-old woman’s throat was slit and her 87-year-old husband was stabbed and beaten to death – would be the first Islamist attack in Austria, which has so far avoided the jihadist assaults seen elsewhere in Europe.

The killings “clearly had an Islamist background”, Sobotka told a press conference in Vienna on Wednesday, adding that the 54-year-old suspect, who handed himself in to police, “is clearly a radicalized Muslim”.

Police had said on Tuesday that the murders did not initially appear to be an Islamist attack, with investigators focusing on the theory that the suspect harboured resentment against society as well as Austria’s far-right Freedom Party (FPOe).

He knew the victims, having regularly delivered their shopping from a shop run by his wife, and allegedly believed the elderly couple had links to the far-right.

But Sobotka told a press conference that the investigation had taken a turn after searches of the suspect’s home and examination of his electronic data.

He declined to give further details on the evidence against the Tunisian, who had lived in Austria since 1989, or what he had said to investigators.

The Tunisian set fire to the couple’s house before handing himself in to police, and remains in detention.