Four people were killed when Kujtim Fejzulai opened fire with a Kalashnikov in a busy area of the Austrian capital on Monday evening.
Swiss police have arrested two men as part of an investigation into Vienna's terror attack.
Two Swiss citizens, aged 18 and 24 were arrested in the city of Winterthur about 10 km from Zurich, police said in a statement on Tuesday.
"The two men were arrested on Tuesday afternoon in coordination with the Austrian authorities," Zurich cantonal police said.
"The extent to which there was a connection between the two arrested persons and the alleged assassin is currently the subject of ongoing clarifications and investigations which are being carried out by the responsible authorities."
Zurich cantonal police, members of the Federal Police and the city police in Winterthur were involved in the law enforcement operation, the statement said.
Der Attentäter hat 4 Todesopfer auf dem Gewissen, 22 Personen wurden verletzt. Mein aufrichtiges Beileid und meine tiefe Anteilnahme gelten den Opfern und ihren Angehörigen.— Karl Nehammer (@karlnehammer) November 3, 2020
The suspect was identified as a 20-year-old Austrian-North Macedonian dual citizen with a previous terror conviction for attempting to join the Daesh terrorist group in Syria.
Police searched 18 properties as well as the suspect's apartment, detaining 14 people associated with the assailant who are being questioned, Interior Minister Karl Nehammer said.
The attacker, identified as Kujtim Fejzulai, was armed with a fake explosive vest, an automatic rifle, a handgun and a machete, according to Nehammer.
Before the attack he posted a photograph on a social media account showing him posing with the rifle and machete, Nehammer said.
Fejzulai was sentenced to 22 months in prison in April 2019 but was granted early release in December.
North Macedonia investigates
According to police in North Macedonia, a landlocked country in the Western Balkans, around 150 nationals travelled to fight alongside terrorists 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 Daesh 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.