Slovakia has threatened to freeze relations with Vietnam over the case of a Vietnamese businessman who Germany says was kidnapped by Vietnamese agents and smuggled back home through Slovakia, the Slovak foreign ministry said on Saturday.

German prosecutors have said businessman Trinh Xuan Thanh, who had sought asylum in Germany, was abducted in a Berlin street by Vietnamese secret service agents and taken back to Vietnam, where he was tried and jailed for life.

The alleged incident took place during a visit to Slovakia by Vietnamese public security minister To Lam in July 2017.

Slovakia’s foreign minister met with his Vietnamese counterpart on the sidelines of a UN general assembly meeting last month seeking an explanation but the country has yet to hear back from Hanoi, the ministry said.

“We haven’t yet received a reply from Vietnam,” the ministry said in a statement. Minister Miroslav Lajcak said that unless Hanoi provided a credible explanation of how the kidnapped (Vietnamese) citizen got to Vietnam, bilateral relations between the countries would be frozen.

“Slovakia is a serious state and will draw resolute diplomatic consequences if the suspicions that Vietnam is facing prove to be true.”

The case has also soured relations between Germany and Vietnam and prompted Germany to accuse Vietnam of breaching international law. A German court in July sentenced a Vietnamese man to three years and 10 months in jail after he confessed to helping his country’s secret services kidnap Thanh.

Slovakia sought to distance itself from the incident following a report in Dennik N alleging Thanh was taken in a van from Berlin via Prague to Bratislava, where he was added to the Vietnamese minister’s delegation and left on a Slovak government plane.

Former interior minister Robert Kalinak in August denied any involvement in the kidnapping, calling the media report “science-fiction”.