BELGRADE/PRISTINA (Reuters) - Serbia ordered its troops on full alert on Tuesday and Russia accused Kosovo of provocation after a Kosovan police anti-crime operation in a region populated mainly by Serbs led to clashes.

Kosovo police secure the area near the town of Zubin Potok, Kosovo, May 28, 2019. REUTERS/Laura Hasani

At least 19 people were arrested and a Russian U.N. official detained in the operation. Five police and six Serb civilians were wounded in fighting, Kosovan official said.

The incidents signaled rising tensions in four Serb-majority municipalities in northern Kosovo, parts of which remain largely outside control of Pristina and pledge allegiance to Belgrade.

The United Nations peacekeeping mission in Kosovo appealed for calm.

Belgrade said it viewed the Kosovan police operation as an attempt by Pristina to take control of northern parts of Kosovo which border Serbia.

Serbian President Aleksandar Vucic told parliament that Belgrade would try to “preserve peace and stability” but remained ready to react.

“As the supreme commander, I have placed our army units in full combat readiness, if there is any serious endangering of order and people in the northern Kosovo, they will protect our people,” he told deputies.

Kosovan Foreign Minister Behgjet Pacolli said the operation had been carried out against criminal groups in northern Kosovo, where cross-boder smuggling is rampant.

“It was normal work of our police and I believe it’s not the last operation in Kosovo. Maybe today or the next days we will keep fighting the organized crime,” Pacoli told reporters in the Slovak capital Bratislava.

In Pristina, police chief Rashit Qalaj said a total of 19 Kosovan police officers had been arrested on suspicion of smuggling goods into the country. Eleven were ethnic Serbs, four ethnic Albanians and four were Bosniaks, he told a news conference.

Law enforcement officers had faced “armed resistance”, Qalaj said. Five policemen were wounded, one from a gunshot. Six Serb civilians were also hurt, he said.

Majority-Albanian Kosovo declared independence in 2008, almost a decade after NATO air strikes wrested control of the territory away from Belgrade to end a counter-insurgency campaign by Serbian security forces.

But Serbia, which under its constitution considers Kosovo an integral part of its territory, has been blocking Kosovo from membership of international institutions including Interpol and UNESCO. It also still provides financial aid to Serbs in Kosovo.

Slideshow ( 5 images )

RUSSIAN DETAINED

Two United Nations employees, one of them Russian, were also detained in the Kosovo police operation.

Both were later released after demands from the U.N. mission - known as UNMIK - and the Kremlin. They were taken to hospital for treatment.

Qalaj said the Russian and a local staffer had been detained for joining a barricade.

UNMIK was following the developments in northern Kosovo with great concern, U.N. mission chief Zahir Tanin said in a statement.

“I urge all parties to abide by the principles of rule of law and dignity for all to life and liberty, and to help restore calm and security in the area,” he said.

Moscow, a close ally of Serbia, had wasted no time in demanding the immediate release of the Russian and criticizing the Kosovan government.

“We consider the incursion of the Kosovo-Albanian special forces into the region’s north...as yet another provocation from Pristina aimed at intimidating and squeezing out the non-Albanian population and establishing control over these areas by force,” the Russian foreign ministry said in a statement.

The NATO peacekeeping force in Kosovo (KFOR) said it was ready to intervene if necessary and also appealed for calm.

“Because of the political sensitivity of the moment...KFOR invites all the parties to deal with the disputes peacefully and responsibly, without any use of force or violence,” NATO said.

A day earlier, Serbia’s Vucic had said Serbia had lost control over Kosovo and called for a compromise solution between Belgrade and Pristina to end the stalemated conflict.

(The story corrects to show police chief Qalaj, not not U.N. mission chief Zahir Tanin, said U.N. employees were arrested for joining barricade.)