The European Union has raised concerns over the construction of a control area on Austria's border with Italy. Greece, meanwhile, is being urged to improve its border controls or risk exclusion from the Schengen Zone.
Austrian police said on Tuesday that construction work on concrete foundations for a planned control area were underway off the northbound motorway at the Brenner pass in the Alps.
"If these plans should materialize then we will have to look at them very seriously. The Brenner pass is essential for freedom of movement within the European Union," European Commission spokeswoman Natasha Bertaud said on Tuesdsay, adding that EU Migration Commissioner Dimitris Avramopoulos would discuss the construction work with Austrian Interior Minister Johanna Mikl-Leitner.
"The Commission is very concerned," she said.
Since receiving 90,000 asylum claims last year, Austria has adopted an increasingly hard-line stance toward to the arrival of refugees, with Vienna having already stepped up controls along its borders to Slovenia and Hungary.
Greece faces Schengen zone exclusion
In a joint letter to Avramopoulos, Italy's Foreign Minister Paolo Gentiloni and Interior Minister Angelino Alfano demanded that he urgently raise the suspicions about new controls with Vienna.
The Italian ministers said the Austrian actions "did not appear to be based on the facts", adding that Mikl-Leitner had "presented no data showing an alleged increase in the migrant flow from Italy."
The growing concerns over Austria's border controls came as the EU said it had given Greece until April 26 to sharpen control over its external borders. If Athens fails to improve its migrant controls, it runs the risk of being suspended from the Schengen passport-free zone, which has increasingly come under threat in recent months as the EU grappled with its biggest influx of refugees since the Second World War.
Despite a sharp fall in the number of refugees arriving in Europe since the beginning of the year, the Italian coastguard reported on Tuesday that some 4,000 migrants had been rescued from boats in the Strait of Sicily, located between Tunisia and Italy, in the past two days.
A vessel from the EU border agency Frontex and a Greek cargo ship assisted the Italian navy in successfully rescuing all the passengers from 16 dinghies and a rowing boat.