NATO troops in Kosovo patrolled the Serb stronghold of north Mitrovica alone on Tuesday after police withdrew following deadly Serb riots.

Kosovo Serb police followed U.N. officers in suspending normal duties in the Serb north of the flashpoint town, under orders from the NATO-led peacekeeping force and U.N. mission still in charge of the newly-independent state.

French, Belgian and Spanish troops in armoured personnel carriers secured the area, and 150 U.S. troops were deployed on the southern, Albanian side of Mitrovica.

The town was still tense having been rocked by the worst violence since Kosovo's ethnic Albanian majority declared independence from Serbia on Feb 17 with Western backing.

Backed by Russia, Serbia has rejected the secession, and Western officials alleged Belgrade's involvement in the unrest in the Serb-dominated strip of north Kosovo.

A senior U.N. source said the mission was "keeping a close eye" on the growing influence of unofficial Serb security structures in north Mitrovica.

Serb riots involving automatic gunfire and hand grenades on Monday killed one Ukrainian police officer serving with the U.N. and left dozens of U.N. police and NATO soldiers injured. The Ukrainian officer died of shrapnel wounds.

The violence was sparked by a U.N. police operation to retake a U.N. court seized three days earlier by Serbs. U.N. officials said Serbian police personnel were involved.

"Of the 40 or so people occupying the building, some were identified as Serbian Ministry of Interior officers," U.S. diplomat Larry Rossin, the deputy head of the U.N. administration in Kosovo, told a news conference.

The senior U.N. source said the mission had intelligence that Serbs had been planning to seize control of the U.N.-run police station adjacent to the court, in a fresh challenge to U.N. and NATO authority in the region.



RED LINE

U.N. police and civilian staff were withdrawn on Monday. On Tuesday, three dozen Kosovo Serb police officers carried their holdalls and flak jackets out past Belgian armoured cars guarding the perimeter to the parking lot.

"Following yesterday's events KFOR has taken over authority for north Mitrovica and occupied the northern police station. U.N. police have ordered us to stay at home until further notice," Captain Milija Milosevic told Reuters.

KFOR commander General Xavier Bout de Marnhac said Monday's riots had "crossed a red line with the deliberate intent to kill people - you know Molotov cocktails, fragmentation grenades and direct fire" aimed at U.N. and KFOR personnel.

"We are not going to tolerate that," the general told a news conference in the Kosovo capital, Pristina.

The violence highlighted the risk of the new country's partition along ethnic lines and cast further doubt on the deployment in the north of a European Union rule-of-law mission in the coming two months.

The main bridge over the river separating the Serb north from the Albanian south remained closed. Razor-wire and upturned garbage containers on the Serb side blocked the way. NATO soldiers in armoured personnel carriers secured the line.

About 120,000 Serbs remain in Kosovo among 2 million ethnic Albanians. Almost half live in the north, adjacent to Serbia and in complete isolation from Pristina. They reject the incoming EU mission as "occupiers".

Kosovo has won recognition from the United States and most EU members. Serbia has Russian support.

"We have warned that this step would inevitably have negative consequences. It happened," Russian Foreign Minister Sergei Lavrov said at a joint news conference with U.S. Secretary of State Condoleezza Rice in Moscow.

Rice said: "We do agree that all sides should refrain from violence and that all sides should refrain from any provocation and we are sending messages to all sides."

Serbia has offered to govern the ethnic Serb areas, senior diplomatic sources told Reuters on Tuesday, in a plan that would effectively partition the newly independent state.

The proposal was made at the weekend by Serbia's Minister for Kosovo, Slobodan Samardzic, but was rejected by the U.N. mission in Kosovo, they said.

The Brussels-based think tank International Crisis Group said in a report the EU and NATO would have to send a "clear message" to Serbia and Russia that they would not permit Kosovo to be divided and become "another frozen conflict".