Croatia launched an investigation on Thursday into new allegations that its police orchestrated violent pushbacks of migrants outside European Union borders -- an unlawful practice under EU law.

       The announcement came after leading European media outlets released footage purporting to show a masked Croatian police officer beating up young asylum-seekers with a stick at the country's border with Bosnia.

       The investigation was conducted over 8 months by Lighthouse Reports, a collaborative journalism platform, with several media outlets including Libération, Der Spiegel and ARD.

       EU 'extremely concerned'

       Earlier on Thursday, EU Home Affairs Commissioner Ylva Johansson called the reports “shocking,” and said she was “extremely concerned.”

       “This needs to be investigated, but they seem to indicate some kind of orchestration of violence at our external borders,” Johansson said.

       The Council of Europe's Commissioner for Human Rights, Dunja Mijatovi？ tweeted Thursday that it was “high time” CoE members “investigate effectively, take action, hold each other to account & end such serious” human rights violations.

       The Lighthouse investigation also reported alleged border pushbacks by Romanian police and Greek coast guard units. Greece's migration minister denied the allegations. There was no immediate response from Romania.

       'EU complicit,' says Amnesty

       Reacting to the report, Jelena Sesar, Balkans Researcher at Amnesty International said it offered "the latest evidence that unlawful pushbacks and violence against asylum-seekers and migrants are commonplace at the EU’s external borders".

       “While the officials’ clothes are deliberately stripped of identifying insignia, it is clear that their uniforms, weapons and equipment are identical to those used exclusively by Croatia’s special police, which has been notorious for conducting violent pushbacks for years now,” Sesar went on.

       The European Commission has repeatedly said it was opposed to pushback practices and made clear to member states that they were illegal.

       But according to Amnesty, the EU's executive "continues to turn a blind eye to the staggering violation of EU law, and even continues to finance police and border operations in some of these countries".

       "European Commission funding has been used by Croatian authorities to buy police equipment and even pay the salaries of border officials, rendering the EU complicit in these violations,” Sesar said.