Austria has suffered its first Islamist attack after an elderly couple were beaten and stabbed to death by a Tunisian man last week, the government has said.

An Hildegard Sch., 85, died after having her throat slit in the northern city of Linz on Friday while husband Siegfried, 87, was stabbed and beaten to death with a stick covered in screws.

The news comes as the country shelved plans to send 750 troops to its border with Italy to head off a potential influx of migrants.

Interior Minister Wolfgang Sobotka said on Wednesday that the 54-year-old Tunisian 'had an Islamist background' and 'is clearly a radicalised Muslim'.

Interior Minister Wolfgang Sobotka said on Wednesday that the Tunisian man suspected of murdering an elderly couple last week 'is clearly a radicalised Muslim'

Hildegard Sch., 85, died after having her throat slit in Linz (file image) on Friday while husband Siegfried, 87, was stabbed and beaten to death with a stick covered in screws

It was initially thought the suspect, who has been living in Austria since 1989, acted out of a political motive - wrongly believing the elderly couple to be involved with Austria's far-right Freedom Party.

But following a search of the Tunisian man's home and electronic devices, investigators concluded the killings were related to radical Islam.

The man had known the elderly couple for some time, regularly delivering them groceries from a vegetable shop run by his wife, the Kurier newspaper reported.

The couple were friendly with the suspect and had even helped him out financially, it was reported.

Following the killings, the man set fire to the couple's house and thought about drowning himself in the Danube river, before deciding to go to police instead.

Chancellor Christian Kern urged an investigation 'without delay' into the extremist threat to determine 'where similar risks exist and how to combat them efficiently'.

Austria had threatened to send hundreds of troops to the Brenner Pass, along the border with Italy, to head off a potential influx of migrants (pictured, police face off against anti-border protesters in Brenner in 2016)

The troops and four armoured vehicles would have been used to block roads and impose checks on those attempting to cross through the Brenner Pass, but Austria has backed away from the idea after Italy threatened to cut security cooperation

The news comes after the Austrian government floated the idea of sending hundreds of troops and armoured vehicles to its southern border with Italy, amid fears that migrants will try to cross en-masse after arriving there from North Africa.

So far this year an estimated 100,000 people have arrived in Europe, most of whom were smuggled out of Libya in rickety boats, with 85,000 ending up in Italy.

But Austrian ministers backed away from that stance yesterday after Rome made its outrage clear and threatened to cut security cooperation, The Local reported.

Austria has so-far been spared a major terror attack, unlike its European neighbours, even though a relatively high number of Austrians have left to wage jihad abroad.

The interior ministry estimates that 300 have quit Austria or tried to leave in order to fight in Syria or Iraq - a high figure considering the country only has a population of 8.7million.

The vast majority of migrants arriving in Austria come via the Central Mediterranean Route (in red), travelling on boats from Libya before finding their way to the border through Italy. Some, though not many, sail to Calabria from Egypt or Turkey, before again travelling north to Austria. Those fleeing war in the Middle East mostly take the Western Balkans Route, though face a difficult time crossing the Turkish border under a deal struck between EU leaders and Erdogan

There is no indication that the man suspected of murdering the elderly couple had travelled abroad to fight alongside extremist groups.

Most of those accused of jihadist links in Austria have been of Chechen or Bosnian origin.

Last year Austrian courts convicted 36 people of 'belonging to a terrorist group', including Mirsad Omerovic, a jihadist of Bosnian origin considered the central figure in Austria's extremist scene.

Austrian authorities have poured more resources into anti-terror operations since 2014, with 14 people arrested in January raids in Vienna and second city Graz, accused of links to the Islamic State group.

The same month, authorities announced they had foiled an imminent attack, arresting an 18-year-old Austrian.

Austria is gearing up for legislative elections in October, which are being closely fought between the social democrats, conservatives and the far-right.