Two Serbian warplanes flew close to a border crossing with its former province of Kosovo on September 26 amid an intensifying dispute over license plates as U.S. and European Union officials scramble to calm the situation.
Serbs on September 20 began blocking two main roads leading into Kosovo to protest Pristina's ban on cars with Serbian license plates.
Pristina said its move mirrors a decision by Belgrade more than a decade ago when Kosovo declared its independence from Serbia.
The tensions have boiled up into acts of violence with Kosovo on September 25 accusing Serbs of attacking two offices run by Kosovo's Interior Ministry, including setting one of them on fire.
There were no reports of casualties.
Kosovo's Prime Minister Albin Kurti said both incidents were intentional, accusing Serbia of "encouraging and supporting" attacks on the state of Kosovo.
Pristina has moved special units of the Kosovo police to the two border crossings.
Meanwhile, helicopters serving the NATO peacekeeping force in Kosovo, KFOR, have also been making regular flights over the area since the dispute erupted.
Media reported seeing Serbian jets circling the area on September 25.
In an effort to stem to tide of rising tensions, the U.S. State Department announced it will send Gabriel Escobar, its top official overseeing the Western Balkans, to Brussels this week to participate in European Union-led talks between the two countries.
"The United States is working with the EU, NATO, and the Governments of Kosovo and Serbia on immediate steps to de-escalate the situation and avoid actions which increase tensions, jeopardize progress under the EU-facilitated Dialogue and adversely impact the everyday lives of citizens," the State Department said in a statement to RFE/RL.
"We support the EU's offer to host discussions this week on this and other issues and encourage Kosovo and Serbia to re-engage openly, seriously, and immediately," the State Department said.
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.
Tensions between Kosovo and Serbia are now at their highest for years despite an agreement reached last year at the White House to improve economic ties, including allowing the free flow of goods and people between the two countries. .
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.
Kosovo's independence is recognized by 110 countries -- including the United States, Britain, and most Western states.