Nato strongly condemned an "unprovoked" attack that injured 25 peacekeepers in Kosovo on Monday, as tensions flare in the Balkan nation.
Clashes erupted as Serb protesters demanded the removal of recently elected ethnic Albanian mayors.
The Nato-led Kosovo Force mission said it faced "unprovoked attacks" while dealing with the crowd.
"Violence must stop immediately," Nato said. "We call on all sides to refrain from actions that further inflame tensions, and to engage in dialogue."
The alliance said that such actions were "totally unacceptable".
More than 50 Serbs were injured during the clashes. Two were seriously wounded and one is in a critical condition, Serbian state-run public broadcaster RTS said.
Italy's Foreign Minister, Antonio Tajani, said three of the country's soldiers were seriously wounded, and Prime Minister Giorgia Meloni joined Nato in calling for "all parties to take a step back to lower tensions".
Kosovo's Serbs boycotted last month's elections in northern towns, which allowed ethnic Albanians to take control of local councils despite a tiny turnout of less than 3.5 per cent of voters.
Kosovan Prime Minister Albin Kurti's government officially installed the mayors last week, defying calls by the EU and the US, which have both championed the territory's 2008 independence from Serbia, to ease the tension.
Tension between Kosovo and Serbia - in pictures
Many Serbs are demanding the withdrawal of Kosovo police forces, whose presence in northern Kosovo has long sparked resistance, and the ethnic Albanian mayors they do not consider to be their true representatives.
Early on Monday, groups of Serbs clashed with Kosovo police in front of the municipal building in the Serb-majority town of Zvecan and tried to force their way into the building.
Police responded by firing tear gas, AFP reported.
Nato-led peacekeepers in the KFOR mission at first tried to separate protesters from the police, but later started to disperse the crowd using shields and batons, it reported.
Several protesters responded by hurling rocks, bottles and Molotov cocktails at the soldiers, but were quickly repelled a few hundred metres away from the Zvecan municipal building.
"While countering the most active fringes of the crowd, several soldiers of the Italian and Hungarian KFOR contingent were the subject of unprovoked attacks and sustained trauma wounds, with fractures and burns due to the explosion of incendiary devices," KFOR said.
Eleven Italian soldiers were injured with "three in a serious condition", Mr Tajani said.
"We will not tolerate further attacks against KFOR," said Ms Meloni.
"It is essential to avoid further unilateral actions by the Kosovo authorities and for all parties to take a step back to lower tensions."
The Commander of the KFOR Mission, Gen Angelo Michele Ristuccia, condemned the "unacceptable" attacks and said KFOR would "continue to fulfil its mandate impartially".
Kosovo police said "organised" demonstrators rallied in northern Kosovo towns, home to many ethnic Serbs who reject Kosovo's independence.
"The protesters, using violence and throwing tear gas, tried to cross the security cordons and make a forced entry into the municipality" building in Zvecan, Kosovo police said.
"Police were forced to use legal means, such as [pepper] spray, to stop the protesters and bring the situation under control."
Kosovo unilaterally declared independence from Serbia in 2008, and Belgrade and its key allies Russia and China have refused to recognise it, effectively preventing Kosovo from having a seat at the UN.
Serbs in Kosovo remained largely loyal to Belgrade, especially in the north, where they make up a majority and reject every move by Pristina to consolidate its control over the region.
KFOR said it had bolstered its presence in northern Kosovo after the latest developments and urged Belgrade and Pristina to engage in an EU-led dialogue to reduce tensions.
"We call on all sides to refrain from actions that could inflame tensions or cause escalation," KFOR said.
Police had already used tear gas on Friday to disperse Serbs in northern Kosovo who protested against the installation of the mayors.
Belgrade responded by placing its army on high alert and ordered forces towards the Serbian border with Kosovo.
Russia's Foreign Minister Sergey Lavrov, speaking on a visit to Kenya, said that the "Serbs are fighting for their rights in northern Kosovo".
"A big explosion is looming in the heart of Europe, where Nato in 1999 carried out an aggression against Yugoslavia," Mr Lavrov said.
He was referring to the 1999 Nato intervention against Belgrade that effectively ended the war between Serb forces and ethnic Albanian guerrillas.
The US ambassador and EU envoy have summoned the ethnic Albanian mayors to a meeting in Pristina in a bid to ease tension.
Two media teams from Pristina reported that protesters had slashed their tyres and spray-painted their vehicles.
A local journalists' association called on law enforcers to provide a safe working environment for the media.
