UNITED NATIONS, United States (AFP) - UN Secretary-General Ban Ki Moon on Monday called for calm to return to Macedonia after violence left 22 dead in the worst clashes since the country's 2001 ethnic conflict.

Ban said in a statement that he was alarmed by the weekend clashes in the northern town of Kumanovo and urged all sides to "cooperate to restore calm and to fully investigate the events in an objective and transparent manner."

He appealed for those involved to "exercise maximum restraint and to refrain from any rhetoric and/or actions that may escalate tensions further."

The violence in Kumanovo, some 40 kilometers north of Skopje, raised concerns about an upsurge in ethnic fighting in the volatile Balkan region.

A Macedonian prosecutor said Monday that 18 citizens of Kosovo were among 30 men charged over the weekend shootout that killed 22, including eight policemen.

"Out of 30 people charged 18 are Kosovans, 11 are Macedonian citizens, two of whom are living in Kosovo, and one is from Albania with residence in Germany," the prosecutor said in a statement.

The accused, most of whom entered Macedonia illegally, have been charged with terrorism offences after the shootout in Kumanovo.

Kosovo condemned "any involvement" of the breakaway territory's citizens in the violence. Kosovo's President Atifete Jahjaga and Prime Minister Isa Mustafa said in a joint statement they "express their deep concern... and condemn any involvement of the citizens of the Republic of Kosovo in the incident in the Republic of Macedonia."