Austria's center-left on Tuesday begins the search for a new leader and new direction after a sharp drop in support, at the hand of the populist far-right, forced Chancellor Werner Faymann to quit.

Analysts said this new departure might even see Faymann's Social Democrats (SPOe) taking the radical and dangerous gamble of dropping its historic opposition to a tie-up with the far-right.

The district of Simmering is archetypal "Red Vienna", its imposing council housing blocks, named after workers' heroes of the past, testament to almost a century of state largesse under the left.

But last year this socialist utopia became the first part of the Austrian capital to be run by the far-right Freedom Party (FPOe), the populist movement turning politics on its head and whose candidate is tipped to become president on May 22.

The head of Austria's anti-immigration far-right apologized Friday for claiming a newspaper faked a photo of an anti-refugee protest by his party, donating 9,000 euros ($10,300) to a migrants charity.

"A close inspection of the matter has now shown that this claim was not accurate. With an expression of my regret I hereby withdraw it," Heinz-Christian Strache of the Freedom Party (FPOe) said on Facebook.

The Austrian parliament on Wednesday adopted one of Europe's toughest asylum laws, as the country's political leaders struggle to halt the surging far-right which is leading in presidential polls.

The hotly-disputed bill, which passed by 98 to 67, allows the government to declare a "state of emergency" if the migrant numbers suddenly rise and reject most asylum-seekers directly at the border, including from war-torn countries like Syria.

Austria will reintroduce controls along its border with Italy unless the migrant flow through the area is drastically reduced, Foreign Minister Sebastian Kurz warned in an interview published Wednesday.

Italian Prime Minister Matteo Renzi last week insisted Italy was not facing an "invasion" after a spike in migrant boat crossings from Libya exacerbated fears it could become the main entry point into Europe.

Austrian prosecutors said Monday they are probing a possible link between a Pakistani held in Salzburg in connection with last November's terror assaults in Paris and the 2008 attacks in the Indian city of Mumbai.

"Leads pointing to this are being looked into," prosecutors in Salzburg said, adding however that the identity of the Pakistani suspect, who has been in custody since December in the western Austrian city, has not been confirmed.

Reducing the flow of migrants is a "question of survival" for the European Union, Austria's interior minister said Wednesday as she pressed Balkan countries in Vienna to help cut the record influx.

"We have to reduce the influx now. This is a question of survival for the EU," Johanna Mikl-Leitner said after talks in Vienna with ministers from nine countries along the west Balkans route from Greece towards northern Europe.

Austrian prosecutors said Thursday they were investigating four people being held in custody for possible links to the November 13 Paris terror attacks, two more than previously confirmed.

Calling the investigations "highly complex", Salzburg prosecutors said that all four are believed to belong to the so-called Islamic State extremist group, which claimed responsibility for the Paris attacks.

The European Commission urged Austria Thursday to reconsider its plans to limit asylum claims which it warned would be "plainly incompatible" with European Union laws.

European migration commissioner Dimitris Avramopoulos sent the complaint in a letter to Austria's Interior Minister Johanna Mikl-Leitner who said Wednesday the country would cap the daily number of asylum claims at 80.

Austrian Chancellor Werner Faymann said Wednesday he expected Germany to follow his tougher migrant stance and clamp down on the number of asylum seekers allowed into the country.

Vienna announced Tuesday it would step up controls at existing checkpoints along its southern borders with Italy, Slovenia and Hungary to slow down the influx of migrants and refugees trekking up along the Balkans.