(BRUSSELS) - NATO promised Monday a firm response to any further unrest in Kosovo while the EU ruled out delaying a European police mission there, following clashes between UN police and angry Serbs which left over 100 people injured.

Both the European Union and the North Atlantic Treaty Organisation voiced concern over the clashes in Kosovo, where UN police stormed a court occupied by Serbs opposed to the territory's independence, and called for restraint.

NATO vowed to "respond firmly" to any further unrest in Kosovo and urged all parties to exercise restraint, the alliance's chief spokesman said.

"NATO condemns, in the strongest terms, violence that we have seen today," spokesman James Appathurai said. "NATO will respond firmly to ensure a safe and secure environment."

His remarks came after UN police were forced to withdraw Monday from the Serb-populated part of this flashpoint Kosovo town of Mitrovica after coming under attack as they stormed a court occupied by Serbs opposed to independence.

More than 100 people including 33 international security force members were hurt amid gunfire and a suspected grenade blast after they moved in to regain control of the UN-run tribunal in the northern Kosovo town near the border with Serbia.

At least 27 of the wounded UN police were Polish, according to a police spokesman in Warsaw who said they had been pelted with rocks, homemade explosives and possibly shot at.

EU foreign policy chief Javier Solana expressed his "deep concern" at the violence in Mitrovica and called for calm.

Speaking on the margins of an EU meeting in Ljubljana he ruled out any delay in deploying a 2,000-strong peace and justice mission to Kosovo in the wake of violent clashes.

"The mission is continuing the deployment according to the calendar that has been established. Nothing for the moment has changed," he added.

The first elements of the EU peace and justice mission EULEX mission began arriving in Kosovo last week.

Kosovo's government unilaterally declared the independence of the ethnic Albanian-majority province from Serbia on February 17 and has since been recognised by many Western countries.

However Serbia and Kosovo Serbs vehemently reject the move as illegal.

EU member Britain called on "all sides to reject violence".

While acknowledging "how difficult Kosovan independence is for Serbia and Kosovo's Serbs" a British Foreign Office spokesman surged them to "address their genuine concerns through political dialogue."

The European Commission also appealed for calm.

"We are very concerned about the tense situation in north Mitrovica. We regret the attacks against the UN police and KFOR personnel. We call for restraint," a Commission spokesman told reporters in Brussels.

The EU's Slovenian presidency strongly condemned the violence saying; "a multi-ethnic Kosovo can only be built through cooperation of all its communities, while fully respecting the rule of law and democracy."

Meanwhile Russia, strongly opposed to Kosovo's independence, called for a return to international talks on its status, saying the latest unrest was a result of the territory's unilateral independence declaration.

"It's clear that the situation can only be normalised by returning the Kosovo process to the framework of international law, with the aim of finding a mutually acceptable solution based on dialogue between Belgrade and Pristina," Russia's foreign ministry said in a statement.

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