The European Union, the North Atlantic Treaty Organization and the head of the United Nations called for calm in Macedonia after weekend events that left eight police and 14 civilians dead.

The government said over the weekend that the deaths occurred in an “antiterrorist operation” that was launched against one of the “most dangerous terrorist groups in the Balkans.”

EU enlargement commissioner Johannes Hahn said Monday “We are all concerned what happened over the weekend. We urge all involved parties…to collaborate in clarifying what has happened, who is responsible for this.”

He told a press conference that the killings “should not be seen as an opportunity” to escape from “resolving the fundamental problems the country is facing,” nor can the events end up by “introducing further complexity—an ethnic conflict” in the country’s already-difficult situation. He urged the government and opposition to start working together.

In recent months, leaked wiretaps that appeared to expose government corruption and interference with the judiciary have caused public outrage and sparked street protests calling for the government’s resignation.

Details of the weekend events remain sketchy, but Macedonia’s Interior ministry said some of the dead civilians were wearing uniforms with insignia of the disbanded ethnic Albanian Kosovo Liberation Army, which fought for Kosovo’s independence in the late 1990s. The Interior ministry said the police managed to “neutralize” the terrorist group.

Macedonia’s state-run news agency, MIA, said Monday a court in Skopje, the capital, had ordered 30-day detention for 30 individuals allegedly linked to the incident, including 18 Kosovo nationals. The charges against them were posing a terrorist danger to order and security in Macedonia, MIA reported. An Interior Ministry representative wasn’t immediately available to comment on the charges.

Ethnic Albanians constitute the largest minority population in Macedonia, a country of just over two million people. According to the country’s last census in 2002, slightly more than 25% of the population was ethnic Albanian.

NATO Secretary-General Jens Stoltenberg called on the government in Skopje to mount a “transparent investigation” into the events and keep dialogue open with authorities in neighboring Kosovo. Macedonia hopes to join NATO one day.

Kosovo’s Foreign Minister Hashim Thaçi said his government is in close touch with Macedonia’s government and has taken measures to secure Kosovo’s border with Macedonia. Kosovo, which has a majority ethnic Albanian population, is also seeking to eventually join the EU.

“I’m genuinely concerned over the violence that erupted in Macedonia over the weekend. I visited Skopje recently, met all the senior leadership and Kosovo looks at Macedonia as an ally and a partner,” Mr. Thaçi said. “Let me be loud and clear, those forces that are working to bring instability to Macedonia are enemies of stability in all of the Balkans, Kosovo included,” he said.

Macedonia has failed to advance on its NATO and EU membership tracks, partly because of a continuing dispute with Greece about what the country should be called. Greece has repeatedly blocked Macedonia’s EU bid because the word “Macedonia” coincides with the name of the adjacent Greek region. The provisional name of the country is the “Former Yugoslav Republic of Macedonia.”

EU officials have acknowledged that the name issue, by blocking Macedonia’s EU path, has weakened incentives to push democratic reforms, helping create the current political and economic stalemate.

However, the EU’s former point-man in Macedonia between 2005-10, Erwan Fouéré, said the government in Skopje is using the name issue as an excuse to turn increasingly repressive at home.

“There have been many missed opportunities with this government,” he said. “As the protests over the last weeks and months have shown, there is a united call across ethnic divides, bringing together Albanians and Macedonians in rejecting the government’s behavior.”

Mr. Fouéré, who is now a senior research fellow with the Centre for European Policy Studies, a Brussels-based think tank, says Macedonia, an EU candidate since 2005, is “sort of forgotten, at the bottom of the EU priority list.” He said he hoped that the event would shift some attention to the country.

U.N. Secretary-General Ban Ki-moon urged the government and political leaders to cooperate to restore calm “and to fully investigate the events in an objective and transparent manner.”