The US has announced measures against Kosovo for overlooking its advice to try not to bring pressures up in larger part of Serb northern regions.

It has criticized Kosovo's decision to install ethnic Albanian mayors in northern Kosovo "by forcible means".

Kosovo has been ousted from partaking in an ongoing American-led military exercise in Europe.

Police and Nato troops conflicted with Serb protesters in Zvecan, north Kosovo, on Monday.

Protesters had tried to invade a government building amid unrest over the installation of ethnic Albanian mayors in areas where Serbs make up the majority of the population.

Nato is to convey 700 extra soldiers to Kosovo after saying 30 of its peacekeepers and 52 protesters were hurt in the clashes in Zvecan.

The crisis dates back to April when ethnic Serbs boycotted local elections in north Kosovo - allowing ethnic Albanians to take control of local councils with a turnout of less than 4%.

Like the US, the European Union has accused the Kosovan authorities of destabilizing the situation in north Kosovo and warned against any actions that could inflame ethnic tensions there.

Kosovo declared independence from Serbia in February 2008, after years of strained relations between its Serb and mainly Albanian inhabitants.

It has been recognized by the US and major EU countries. But Serbia, backed by its powerful ally Russia, refuses to do so - as do most ethnic Serbs inside Kosovo.

While ethnic Albanians make up more than 90% of the population in Kosovo as a whole, Serbs form the majority of the population in the northern region.

The American ambassador in Pristina, Jeffrey Hovenier, said that the US "foresaw the consequences" of the decision to forcibly install ethnic-Albanian mayors in four majority-Serb municipalities.

The US - a strong ally of Kosovo - said it had "strongly advised" Prime Minister Albin Kurti to change his course of action, but the advice was ignored.

As a result, Kosovo's participation in a Nato exercise, Defender Europe 23, has been canceled.

Mr. Hovenier said the US was considering other measures and currently "has no enthusiasm" to assist Kosovo in its efforts to gain wider international recognition or progress towards membership of the EU and Nato.

Serbia and Kosovo's leaders have traded accusations over the violent scenes.

Serbian President Aleksandar Vucic said Kosovan PM Albin Kurti "alone is responsible" for the disturbances.

In return, Mr. Kurti claimed the protesters in Zvecan were "a bunch of extremists under the direction of official Belgrade".

The alliance's chief Jens Stoltenberg said the violence "must stop".

He strongly condemned "the unprovoked attacks against Kfor troops" - referring to Nato's peacekeeping force in Kosovo.

But ethnic Serbs in north Kosovo have criticized Kfor for failing to prevent armed Kosovo police from forcing their way into municipal buildings and removing Serbian flags.

Tuesday's announcement from Nato provides a significant boost to Kfor's numbers. The 700 additional troops will join the 3,800 who are already on duty in Kosovo.

An additional reserve battalion has been placed on standby and will be ready to deploy within seven days if required.

Kfor's mission is to guarantee the safety and freedom of movement of everyone in Kosovo, regardless of their ethnicity.

So the new troops will face considerable expectations from both sides after this week's disturbances.

Former Nato chief Lord Robertson has accused Serbia of stoking tension in Kosovo.

"The idea that we would withdraw completely from Kosovo can't happen until Serbia begins to acknowledge reality," he told BBC Radio 4's World Tonight program after returning from a visit to Kosovo.

Noting the "salutary warning" from the Americans to the Kosovan authorities, he said a "degree of common sense and a degree of cool diplomacy should've been the order of the day".

"I think the Kosovan authorities should've handled it much better," he said. "The fact that their close friends, like the Americans, are giving them very pointed warnings should make them rethink what they are doing."

He chided both Kosovo and Serbia, saying both had to "sit down carefully and think through what future they want for the people of both countries".