PRISTINA -- Police in Kosovo said on September 25 that two offices run by Kosovo's Interior Ministry have been attacked in the northern part of the country.

The attacks took place in mostly ethnic Serb communities near border crossings that have been blocked by local Serbs to protest Kosovo's ban on cars with Serbian license plates entering the country.

The Interior Ministry's Vehicle Registration Center In the town of Zubin Potok was set ablaze, Kosovar police said in a statement.

Authorities said the fire damaged the ground floor of the building and was thought to have affected Interior Ministry offices there along with the library of the local House of Culture."

In the nearby town of Zvecan, two hand grenades were thrown at the Civil Registration Center in the building of the Municipal Assembly but did not explode, authorities said.

There were no reports of casualties.

Kosovar Prime Minister Albin Kurti said both attacks were intentional, accusing Serbia of "encouraging and supporting" attacks on the state of Kosovo.

"Serbia is using Kosovo citizens to provoke a serious international conflict," Kurti said.

"Individuals or groups whose criminal activity endangers the rule of law and public order are attacking our state and disturbing the peace," Kurti wrote on Facebook. "They are clearly encouraged and supported by Serbia, namely the autocratic regime there."

Ethnic Serbs have used hundreds of vehicles to block two main roads in northern Kosovo near the border with Serbia since Pristina's ban on Serbian license plates came into force on September 20.

Meanwhile, special units of the Kosovar police have been stationed at the Jarinje and Brnjak border crossings.

An AFP correspondent reported seeing Serbian fighter jets fly twice over the border area around noon on September 25.

Serbian military helicopters were seen on September 24 flying several times over the border posts blocked by ethnic Serb protesters.

Helicopters serving the NATO peacekeeping force KFOR have also been making regular flights over the area since the dispute erupted.

Kosovo's ban requires all drivers from Serbia to use temporary printed registration details that are valid for 60 days.

The government in Pristina says the ban resembles measures imposed by Serbia against drivers from Kosovo since 2008, when Kosovo declared its independence from Serbia.

Belgrade does not recognize Kosovo's independence, and many ethnic Serbs in northern Kosovo also consider themselves to be citizens of Serbia.

Kosovo's Interior Minister Xhelal Svecla said the latest attacks will not prevent the government from implementing its ban on Serbian license plates across all the territory of Kosovo.

"These criminal actions show best what would happen at the border crossings in Jarinje and Brnjak if we did not have the presence of special units to ensure order and security," Svecla said on Facebook on September 25. "Despite such actions, we will continue with our full commitment to implement the [Serbian license plate ban] throughout the territory of Republic of Kosovo."

Meanwhile, Kosovo's Defense Ministry is denying reports that the Kosovo Security Force (KSF) is preparing to deploy troops in northern Kosovo.

"The misinformation that the KSF is preparing military troops for intervention in northern Kosovo is completely untrue," the Defense Ministry said in a statement on September 24.

It said such reports were an attempt to "misinform the public and to present a situation of insecurity for our citizens of the Serb community."

Tensions between Kosovo and Serbia are now at their highest for years.

NATO's mission in Kosovo, where troops from the alliance maintain a fragile peace, has called for restraint.

The European Union and the United States have called for dialogue between the two sides on the issue in order to prevent tensions from escalating further.

Kurti has asked Serbia to start recognizing Kosovo car license plates to allow the free movement of people and goods.

Serbian President Aleksandar Vucic has said Kosovo should first remove police units sent by Pristina into northern Kosovo to help enforce the license-plate measures.

Serbia and Kosovo committed in 2013 to a dialogue sponsored by the European Union in an attempt to resolve outstanding issues. But little progress has been made.

Kosovo's independence is recognized by 110 countries -- including the United States, Britain, and most Western states.

But Kosovo's independence is not recognized by Russia, Serbia's traditional ally, and five EU member states.

With reporting by RFE/RL's Balkan Service correspondent Luljeta Krasniqi-Veseli and Reuters