BRUSSELS (AP) — Kosovo’s president on Thursday accused investigators of dragging their feet over an inquiry into attacks on NATO peacekeepers earlier this year in which dozens of troops and police officers were injured, some of them seriously.

President Vjosa Osmani also called on European Union officials to refrain from showing any favoritism in talks next week aimed at improving Kosovo’s tense relations with Serbia.

“Those who attacked NATO on the 29th of May are clearly known to law enforcement agencies,” she told reporters at NATO headquarters in Brussels after talks with Secretary-General Jens Stoltenberg. Video footage, Osmani said, shows that some “are police officers who came all the way from Serbia.”

“They have not been suspended from their jobs,” she said. “They’re not facing any consequences whatsoever.”

The clashes happened after Serbs living in the north of Kosovo boycotted local elections there. When newly elected ethnic Albanian mayors began to move into their new offices, some Serbs tried to prevent them from doing so. Kosovo riot police fired tear gas to disperse the crowds as violence broke out.

Kosovo’s police force is in charge of investigating the incidents, but it’s having trouble convincing local Serbs to cooperate. Kosovo police are sometimes assisted in their work by the EU’s rule of law mission there, EULEX.

Stoltenberg said that 93 peacekeepers were injured, some “with life-altering wounds.” He agreed that the perpetrators should be held to account, but unlike Osmani, he refrained from saying who might be responsible for the attacks. He said the investigation was ongoing.

The NATO-led KFOR peacekeeping force has been stationed in Kosovo since the military alliance launched an air campaign against Serbia in 1999 to stop a bloody crackdown on ethnic Albanians in the former territory. More than 10,000 people died in the violence.

Kosovo unilaterally broke away from Serbia in 2008, but the government in Belgrade has never accepted the loss of its former province.

On Wednesday, the commander of KFOR, Italian Maj. Gen. Angelo Michele Ristuccia, said that his forces “are living a time frame of constant crisis management.” He said that tensions between Belgrade and Pristina are so high that even “the most insignificant event can create a situation.”

The EU has been supervising talks to normalize their ties, but those talks are bogged down. The leaders of Kosovo and Serbia are expected to take part in more negotiations on Sept. 14, but it’s unclear whether they will even meet face to face, such are their differences.

Osmani said Kosovo’s hopes for those talks are “that there will be a balanced approach.” She said that “a balanced approach by the EU intermediators is a precondition for the success of the process. There were times when we didn’t see this balance.”

Last month, senior lawmakers from the United States and Europe called for a change in the Western diplomatic approach toward Serbia and Kosovo amid concern that tensions between the two could rapidly spiral out of control.

They noted a “lack of pressure on Serbia” over the attacks and the detention of Kosovo police. They said the West’s diplomatic response “highlights the current lack of evenhandedness in addressing such flashpoints.”

Stoltenberg said the EU-brokered talks are the best way forward. Asked whether NATO and others in the West are being lenient on Serbia, because the country is helping to supply weapons to Ukraine, he said: “It’s not the case. We have been very clear also in our messages to Belgrade.”

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Llazar Semini contributed to this report from Tirana, Albania.