SARAJEVO, Bosnia-Herzegovina (AP) — Danish aid workers stationed in the Balkans say dozens of migrants have alleged they were brutalized by Croatian law-enforcement officers when they tried to cross into the European Union nation, before being summarily expelled back to Bosnia.

Nicola Bay, the head of the Danish Refugee Council in Bosnia, told The Associated Press Friday that 149 migrants of varying nationalities, independently interviewed by his staff in the country over the past 10 days, reported being exposed to “extremely abusive” treatment by Croatian police.

The testimonies include allegations of brutal and prolonged beatings, of people being stripped naked and being forced to lie like logs stacked on top of each other, Bay said, adding: “In two cases, we have reports of severe sexual abuse.”

Bosnia, which has never truly recovered from its brutal 1992-95 war, became a bottleneck for thousands of Europe-bound migrants from the Middle East, Central Asia and North Africa three years ago when other nations closed their borders and disrupted migration paths through the Balkans.

Upon entering Bosnia, most migrants walk northwest to the country’s highly porous 1,000-kilometer (620-mile) border with Croatia, one of the last gateways to northern Europe.

Bay said that testimonies collected from groups who had not been in contact with each other included the same descriptions of violence.

“The similarities between these accounts are really chilling in that they point to systematic patterns of abuse…(by) men in black uniforms and with black balaclavas” hiding their faces, he added.

Describing the testimonies as “horrifying,” the DRC’s secretary general, Charlotte Slente, urged in a written statement for immediate action "to put a stop to the systematic use of violence.”

“Treating human beings like this … irrespective of their migratory status, cannot and should not be accepted by any European country, or by any EU institution,” Slente added.

Human rights organizations have been accusing Croatia’s police for years of brutality and illegal pushbacks of migrants, which Croatia has consistently denied.

Calls to the Croatian police press office went unanswered Friday. Croatia’s Interior Ministry said earlier this week it was investigating the DRC allegations with the goal of “removing any doubt about the behavior of Croatian police officers or sanctioning and eliminating all irregularities if any occurred.”

Migrants interviewed by the DRC in Bosnia bore visible injuries that were also documented in a series of disturbing photographs shared with the AP.

Separately on Friday, in a makeshift camp in northwestern Bosnia, numerous other migrants were nursing injuries they said were inflicted on them by the Croatian police after they managed to cross into the country this month.

“When they catch us, they start beating us with sticks and kicking us as if we were animals … before taking us back” to Bosnia, a young man from Bangladesh said in the camp close to the border with Croatia where hundreds of migrants are stranded.

The man, who asked not to be identified out of fear of repercussions, said Croatian police also confiscated migrants’ belongings such as mobile phones and money.

Another migrant, who identified himself as Muhammed from Pakistan, claimed Croatian police set dogs on him after he crossed into the country two weeks ago. He showed healing wounds on his arms and legs.

Dunja Mijatovic, the Council of Europe’s Commissioner for Human Rights, voiced concern over the latest allegations, noting that the Croatian government’s customary reaction “has been to dismiss reports published by NGOs or resulting from investigative journalism.”

Mijatovic said in a written statement that despite the Croatian government asserting that all allegations are investigated, "credible reports of such violations continue.”

“Disturbingly, these reports suggest that violence and de-humanizing acts accompanying pushbacks are increasing, and it seems that Croatian law enforcement officers continue to enjoy impunity for such serious human rights violations,” Mijatovic said.