© BMI / Austrian Interior Ministry / AFPFILE PHOTO: Austrian policemen stand near a mosque in Vienna on November 6, 2020.
Austrian authorities watched a meeting in Vienna this summer between foreign Islamists and the jihadist who killed four people last week, and trailed him for days but then stopped, news agency APA reported on Monday.

Austria has acknowledged that "intolerable mistakes were made" in the handling of intelligence on the attacker, a convicted jihadist, who killed four people in a shooting rampage in the centre of Vienna last Monday. He was shot dead by police.

First Vienna said it had mishandled information from Slovakia that the gunman had tried to buy ammunition there in July. Then it admitted he had met people from Germany who were under observation there and who travelled to Austria, and that could have led it to see him as a greater threat.

On Monday it confirmed a report by Swiss newspaper NZZ am Sonntag that he had also met two Islamists arrested in Switzerland in connection with the attack who had travelled to Vienna between July 16 and July 20.

"A meeting took place in Vienna among the people (you) addressed from Germany and Switzerland but there were also people present at the meeting with the later assailant who were arrested in the context of the investigation," Director General for Public Security Franz Ruf told a news conference when asked about the reported July meeting.

"It was a larger circle of people that met. Some spent the night, the rest then left," he added.

Austrian domestic intelligence monitored the meeting and the attacker for days, observing how he and acquaintances picked up the four visitors from Germany and Switzerland at Vienna airport and showed them around the city. But it broke off the tailing operation just as he travelled to Slovakia, APA reported.

Why that operation was halted is unclear, APA said. The Interior Ministry was not immediately available for comment.

"New disturbing failures come in almost by the hour," Stephanie Krisper, a senior lawmaker from the liberal Neos opposition party said on Twitter, referring to the tail.

The head of Austria's main domestic intelligence agency for Vienna has stepped down temporarily pending an investigation into what went wrong.

Austrian intelligence is "traditionally weak and must be strengthened" as part of a previously planned and continuing overhaul, Ruf said.