By Andrew Gray and John Irish

BULBOACA, Moldova The presidents of Serbia and Kosovo insisted on Thursday they want to defuse a violent crisis in northern Kosovo but showed little sign of backing down from their opposing positions.

Arriving at a summit in Moldova of more than 40 European leaders, Serbia's Aleksandar Vucic and Kosovo's Vjosa Osmani did not acknowledge each other even as they stood just metres apart on the red carpet.

Both sides are under international pressure to resolve the latest in a long line of crises between Kosovo's ethnic Albanian-dominated government and ethnic Serbs who are a majority in the north.

Violence flared on Monday after Kosovo authorities, backed by special police units, installed ethnic Albanian mayors in offices in northern municipalities. The mayors had been elected on turnout of just 3.5% after Serbs boycotted local polls.

Osmani said Belgrade was trying to destabilise Kosovo as it had failed to come to terms with Kosovo's 2008 declaration of independence from Serbia.

"We all understand that the real threat in fact is coming from Serbia's denial of Kosovo's existence of a sovereign state," Osmani said.

She accused Vucic of backing criminal gangs in northern Kosovo, which she said were ultimately responsible for clashes that wounded 30 NATO peacekeeping troops and 52 Serb protesters.

"President Vucic needs to stop supporting criminal gangs in Kosovo. That's what he needs to do if he truly wants peace. He's yet to show that," she said.

Serbia has rejected that accusation. As he arrived at the summit at a castle in the Moldovan countryside, Vucic was less forceful than Osmani in his rhetoric.

But he said Kosovo authorities should withdraw "alleged mayors" from the north and declared the Kosovo special police units were there illegally.

"Serbia will do its best and its utmost to de-escalate the situation, which means that we'll try to persuade Serbs to progress calmly and peacefully," he said.

"They're very determined," he added. "They want to see the back of the special police units."

SEPARATE MEETINGS

Ethnic Serbs in north Kosovo have long demanded the implementation of an European Union-brokered 2013 deal to create an association of autonomous municipalities in their area.

Osmani and Vucic were due to meet separately with French President Emmanuel Macron and German Chancellor Olaf Scholz on the sidelines of the summit of the European Political Community, a body of more than 40 countries established last year.

But there was no indication Vucic and Osmani would meet each other. Vucic said he did not even know who was coming to the summit from Kosovo.

Kosovo Prime Minister Albin Kurti has been the driving force behind operations in the north, leading to strong international criticism, particularly from the United States, long Kosovo's staunchest ally.

But Osmani represented Kosovo at the summit.

She said she would be talking to "European leaders who are in favour of peace, in favour of stability and in favour of rule of law," citing Macron and Scholz, but not Vucic.

NATO decided to deploy 700 additional peacekeepers to Kosovo in response to the crisis and the alliance's secretary-general, Jens Stoltenberg, said on Thursday it was ready to send more.

"NATO will remain vigilant. We will be there to ensure a safe and secure environment, and also to calm down and reduce tensions", he told reporters on the sidelines of a NATO foreign ministers' meeting in Oslo.

(Reporting by Andrew Gray, Fatos Bytyci, Ivana Sekularac, Sabine Siebold and John Irish; Editing by Daria Sito-Sucic and Edmund Blair)