The two Iraqis and one Syrian taken into custody on Friday arrived to Austria via the Balkan route last year, the police said on Friday.

Authorities said they believe the refugees fought for or aided "terrorist" groups, police chief Helmut Tomac said, according to the Austrian "Krone" newspaper.

The 27-year-old Syrian reportedly confessed to killing 20 people, including prisoners and Syrian soldiers, while fighting for the al Qaeda-linked Nusra Front.

A 28-year-old Iraqi is suspected of killing several people while fighting for an Iraqi militia in 2014 and 2015. The police believe that the last remaining migrant, a 19-year-old from Iraq, delivered supplies to the same group. He had previously been arrested for stirring up trouble in a refugee home in Tirol, police said.

The 19-year-old has a reputation for being a religious extremist, Austrian public broadcaster ORF reported.

Despite their experiences in the Middle East, there was no indication that the three men were planning terror strikes in Austria or elsewhere in Europe, police chief Tomac said.

Hundreds of suspected jihadists in Austria

Tirol Governor Günther Platter, a member of the far-right ÖVP party, urged the authorities to prosecute the suspects "to the fullest extent of the law."

"We will not allow criminals and terrorists to come to our country and endanger our safety," he said in a statement quoted by "Krone."

"All possible steps must be taken to ensure that the population feels safe, including draconic penalties," he added.

Austrian authorities are currently monitoring 270 suspected jihadis who allegedly traveled to the Middle East to join Islamist militants or made plans to do so.

Two other migrants have been in prison since December for suspected links to men who attacked Paris last year.