World number three Novak Djokovic of Serbia risked political controversy at the French Open after he wrote a letter about Kosovo following his first-round victory on Monday.

Djokovic, who won 22 Grand Slam titles, wrote on camera in Serbian: "Kosovo is the heart of Serbia. Stop the violence."

About 25 NATO peacekeepers were wounded while securing three town headquarters in northern Kosovo in clashes with Serbian protesters on Monday, while Serbia's president put the army on the highest level of combat alert.

"Kosovo is the heart of Serbia – stop the violence", Novak Djokovic wrote on camera after winning the first round of Roland Garros

— Spriter (@Spriter99880) May 29, 2023

The incidents came a day after NATO Secretary-General Jens Stoltenberg called on Kosovo to ease tensions with Serbia, following clashes between Kosovo police and demonstrators opposing Albanian mayors taking office in Serb-dominated areas.

Serbian President Aleksandar Vucic said 52 people were injured on Monday, including 3 in serious condition, while Kosovo President Viosa Osmani accused her Serbian counterpart of destabilizing Kosovo.

Serbia and its traditional ally Russia do not recognize Kosovo's independence, Moscow has blocked the country's bid to become a member of the United Nations, and Serbia still considers Kosovo part of its territory.

Let's go ! Idemo! 💪🏼👍🏼🙌🏼🙌🏼 #RolandGarros

— Novak Djokovic (@DjokerNole) May 29, 2023

Djokovic, 36, told Serbian media that "Kosovo is our cradle, our stronghold and the center of the most important things in our country. There are many reasons why I wrote that on camera."

The French Tennis Federation, which organises the tournament, told Reuters: "There are no official Grand Slam rules on what players can or cannot say. The federation will not issue any statement or take any position on this matter."

Djokovic hopes to avoid any further political distraction at a major tournament after defending his father at the Australian Open in January when he appeared in a video with fans holding Russian flags in the midst of the war in Ukraine.