NATO and the EU called for a return to calm in Macedonia Sunday after clashes between police and an armed group left at least 22 people dead, raising concerns about alleged ethnic-Albanian unrest in the Balkan region.

"I urge everyone to exercise restraint and avoid any further escalation, in the interest of the country and the whole region," NATO Jens Stoltenberg said in a statement.

Macedonia braced for more protests Wednesday after dozens were injured in a night of violent clashes sparked by a long-running political power struggle that threatens to destabilize the country.

The capital Skopje was calm after more than 40 people, mostly police officers, were injured and 30 protesters were detained in the clashes that erupted late Tuesday. A new demonstration was planned for Wednesday evening.

At least 19 people were injured Tuesday, including 15 police officers and a photographer, when an anti-government protest in Macedonian capital turned violent. 

Police used teargas and watercannon to disperse some 1,000 people who gathered in front of the government building in Skopje following an opposition leader's accusation that the cabinet of conservative Prime Minister Nikola Gruevski had covered up the 2011 murder of a 22-year old man beaten by police during post-election celebrations.

At least 14 immigrants from Somalia and Afghanistan were killed in central Macedonia when they were hit by an international passenger train, officials said on Friday.

The train driver reported seeing several dozen people sitting on or near the track at about 10:30 pm (2030 GMT) on Thursday but was unable to stop in time, a local prosecutor said in a statement.

Bitter exchanges between Macedonia's government and the opposition, including wiretapping and claims of million-euro bribes, have pushed the Balkan state into a deep crisis that could further hamper its already stalled bid for EU membership.

Since the beginning of the year, conservative Prime Minister Nikola Gruevski's government and the centre-left opposition have communicated only through public exchanges of accusations.

Macedonian opposition leader Zoran Zaev has accused the government of wiretapping 20,000 people, including politicians, journalists and religious leaders.

Zaev's claims are the latest salvo in a festering dispute between the center-left leader and the conservative government which last month accused him of espionage.   

The OSCE's media freedom representative on Saturday called for the immediate release of a journalist in Macedonia who was sentenced to prison for allegedly revealing the identity of a murder witness. 

Tomislav Kezarovski was arrested late on Friday after the appeals court in Skopje upheld a guilty verdict against him and ordered him back to prison to serve out a reduced two-year term.

With the world on high alert over foreign fighters joining jihadist ranks in Syria and Iraq, Balkan states are launching efforts to clamp down on recruiting in their region, considered fertile ground by Islamists.

Of the more than 20 million people in southeast Europe, more than five million are Muslims, and an economic slump in weak states battered by past wars has fired up some of the disenfranchised.

Macedonian police said Monday they have detained more than 100 Syrian and Iraqi immigrants, among them women and children, hiding in a train transporting coal from the Greek port of Thessaloniki.

"The immigrants are mainly from Syria and Iraq and they came to Greece from Turkey," Ivo Kotevski, spokesman for the Interior Ministry told AFP.

A Macedonian court on Wednesday sentenced six ethnic Albanians to three years in prison each for their role in violent protests that fanned ethnic tensions in the former Yugoslav republic.