More than two years after trial judges acquitted the former prime minister of Kosovo of murder, rape and torture, an appeals panel at the war crimes tribunal in The Hague on Wednesday ordered him to be retried because the intimidation of witnesses had undermined his trial and produced “a miscarriage of justice.”

The ruling against the former prime minister, Ramush Haradinaj, shocked lawyers at the tribunal, which had never been ordered to conduct a retrial and had rarely seen one group of judges criticize another in the strong language of the ruling.

The decision also threatened to aggravate already mounting political tensions between Kosovo and Serbia on the eve of a separate advisory ruling on Thursday by the International Court of Justice on Kosovo’s legal status....