May 28 (UPI) -- Serbia put its troops on alert near the border with Kosovo on Tuesday after Kosovar authorities arrested more than 20 people in raids in a Serb-dominated region, officials said.
Kosovar special forces conducted the raids near Mitrovica, a city in the northern region of Kosovo.
Kosovo declared independence from Serbia in 2008 after fighting a decade earlier. The country's dominant ethnicity is Albanian, but ethnic Serbs are the majority in Mitrovica.
Kosovar authorities said they conducted the raids to crack down on organized crime and smuggling that flourished after Pristina implemented a 100 percent tariff on all Serbian goods entering the country a year ago.
The raids turned violent, with Serbs attempting to block Kosovar special forces using overturned cars, and Kosovar authorities firing shots over civilians' heads and using tear gas.
Six Serb civilians and five Kosovar police officers were injured in the clashes.
Serbia accused the Kosovar government of targeting the ethnic minority population, but the government said Serbs, Albanians and Bosniaks were arrested in the raids.
Serbian President Aleksandar Vucic ordered his country's troops to "full combat readiness."
"If there is any serious endangering of order and people in the northern Kosovo, they will protect our people," he added.
Among those arrested in the raids were two U.N. diplomats -- a Serbian and a Russian -- who were later released.
NATO, which has some 3,500 peacekeeping troops in Kosovo, urged the two countries to "deal with the disputes peacefully and responsibly, without any use of force or violence."
The agency said it is ready to intervene if needed.