BUDAPEST (Reuters) - A United Nations team of rights experts cut short a trip to Hungary, saying it had been illegally denied access to camps where migrants are detained on the country’s southern frontier.

FILE PHOTO: A wire fence is seen next to the village of Roszke, Hungary, March 11, 2018. Picture taken March 11, 2018. REUTERS/Bernadett Szabo/File Photo

The step marks a new low in relations between Hungary and the U.N., which Budapest has accused of spreading lies about the country and harboring a pro-immigration bias.

“UN human rights experts have taken the unprecedented step of suspending an official visit to Hungary after they were denied access to the Roszke and Tompa ‘transit zones’ at the border with Serbia,” it said in a statement on Thursday.

The Hungarian government did not immediately comment.

Hungary, which lies on the southeastern edge of the European Union, has taken a hardline stand on immigration under right-wing Prime Minister Viktor Orban.

His government fortified its southern border with a razor wire fence in the wake of the 2015 migrant crisis, when more than a million immigrants arrived in Europe, hundreds of thousands transiting Hungary.

Budapest subsequently began taking any new arrivals into custody at container camps set up at two border crossings while their asylum claims are pending.

“We have received a number of credible reports concerning the lack of safeguards against arbitrary detention in these facilities which called for a visit,” said Elina Steinerte and Setondji Roland Adjovi, members of the U.N. Working Group on Arbitrary Detention.

The European Court of Human Rights stepped in earlier this year when Hungary was found to have been refusing food to some asylum seekers at the two camps on the Serbian border.

“Unimpeded access to all places of deprivation of liberty including these transit zones must be guaranteed to independent international, regional and national organizations,” the experts said. “This is vital for the protection of the human rights in a country governed by rule of law.”

The U.N. also cited an international agreement that guarantees access to any detained persons for its experts.

Hungary rejects asylum applications from migrants arriving via safe countries. It was also the first European country to quit a U.N. agreement which aims to make migration safe and orderly amid issues of national sovereignty and international cooperation, following a similar decision by the United States last year.