Vehicles from Hungary, Romania and Serbia are now being checked more intensively at the Austrian border, news agency dpa reports, citing statements made by the Austrian Interior Ministry on Sunday (May 21).

Austrian police cooperation with Hungary is also under scrutiny, the agency reports.

The measures come shortly after Austrian officials became aware late last week of Hungarian Prime Minister Viktor Orban's orders to release hundreds* of foreign prisoners jailed for smuggling. The only condition is that they leave Hungary within 72 hours, dpa reported.

The Interior Ministry in Vienna soured to the news of the release, calling the prisoners criminals who had endangered human lives. In April, the landlocked alpine nation announced plans to extend checks at its borders with Hungary and Slovenia by a further six months from May 11.

Last month, a total of about 3,500 new asylum applications were lodged in Austria -- a third less than during the same period last year. The Interior Ministry attributes this to better monitoring of smuggling routes and closer cooperation with countries of origin and transit, dpa reported.

Irregular migration via the Balkan route to Austria mainly passes through Hungary. According to EU border agency Frontex, the Balkan route is currently the second most active migration route to the EU after the Central Mediterranean. Between January and April of this year, Frontex detected more than 22,000 irregular border crossings along the Balkan route, down 21% from a year earlier.

Diplomatic row

Meanwhile, Austria's Foreign Minister Alexander Schallenberg said Monday (May 22) that his ministry would summon the Hungarian ambassador over the release of the migrant smugglers.

"We think this is an entirely wrong signal," Schallenberg told journalists ahead of a EU meeting in Brussels, adding that he demands "full clarification" of the issue from Hungary.

According to the UN Office on Drugs and Crime (UNODC), migrant smuggling is the "facilitation, for financial or other material gain, of irregular entry into a country where the migrant is not a national or resident."

The main difference between migrant smuggling and human trafficking, according to UNODC, is "financial or material benefit" versus the actual exploitation of the victim and their person.

Hungary has one of the worst records on refugee protection in Europe. Just last week, the European Court of Human Rights ruled that Hungary was guilty of violating three underage asylum seekers' rights.

Read more: Hungary supports Serbia in battle against irregular immigration

with dpa, Reuters

*Although the news agency dpa reports that thousands of prisoners will be, or already have been, released, official Hungarian guidance reflects that this number is closer to 700.