The EU, the US, and Nato have urged calm in Macedonia after a firefight with “terrorists” in which 22 people died and which threatens to ignite ethnic tension.

The fighting, over the weekend, cost the lives of eight policemen and 14 gunmen.

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Thirty seven policemen were injured, with authorities saying the death toll could rise. Thirty or so people were arrested.

EU officials contacted by EUobserver say they have little reliable information on what happened.

The incident took place in an ethnic Albanian district of Kumanovo, a town 40km north of Skopje.

It was claimed by a group calling itself the National Liberation Army (NLA), which is thought to be linked to the Kosovo Liberation Army (KLA), the Kosovar guerrilla force which fought Serbia in the 1990s.

The NLA also claimed responsibility for an attack on a Macedonian police station in Goshnice, near the Kosovo border, in October. But it has never published a manifesto or a list of demands.

Macedonian authorities say the Kumenovo group entered the country in early May and planned to attack state institutions, sport events, and shopping malls.

Ivo Kotevski, an interior ministry spokesman, said some of them wore KLA insignia but none of them had ID documents.

President Gorge Ivanov, who cut short his visit to Russia, said on TV: “Police have prevented co-ordinated terrorist attacks at different locations in the country that would have caused serious destabilisation, chaos, and fear”.

Prime minister Nikola Gruevski pointed to a jihadist explanation, saying some of them had combat experience in the Middle East.

He tried to calm ethnic tension. “This is not a Macedonian-Albanian conflict”, he said on TV, adding that “[police] officers from all ethnic groups” took part in the operation.

The Kumanovo region was, in 2001, the scene of inter-ethnic clashes which almost led to civil war prior to the Nato-brokered Ohrid Agreement, a power-sharing accord between Macedonians and Albanians, who count for 30 percent of the population.

The weekend’s violence prompted international appeals for calm.

Nato secretary general, Jens Stoltenberg, said: “It is important that all political and community leaders work together to restore calm and conduct a transparent investigation”.

The EU’s neighbourhood commissioner, Joahnnes Hahn, noted: “I urge all actors for utmost restraint. Any further escalation must be avoided."

The EU, US, Nato, and OSCE missions in Macedonia added in a joint statement “the armed group in Kumanovo is an isolated phenomenon. We strongly believe that it must not be allowed to harm relations within society”.

Kosovo also condemned “the violation of order and security by any individual or group with destabilising aims in Macedonia”.

To make matters worse, the incident took place amid a crisis of confidence in Gruevski’s ruling VMRO-DPMNE party.

The Macedonian opposition, the SDSM party, has, in recent weeks, published a series of wire-tapped conversations implicating VMRO-DPMNE members in criminal activity.

The list includes: the cover-up of a police killing of an anti-government protester, 21-year old Martin Neskovski; manipulation of judges; electoral fraud; and financial mismanagement.

The revelations are believed by EU officials to come from an opposition mole in the intelligence services who rebelled over the goverment’s snooping activities.

But Gruevski's timing of the Kumenovo operation, one week before an anti-government rally on 17 May, has prompted popular theories that it was designed to quash anti-government feeling.