Protesters said extending the so-called "confidence zone," in which people of all ethnic groups should be able to move freely, to the Serb section of town would give ethnic Albanians a green light to force them from their homes.
At issue is who will control Mitrovica's districtstwo areas neatly divided by the Ibar river into Serb-dominated north and Albanian-dominated south. But the tidy geographic division of the town belies the messy realityminority communities, especially a small Albanian enclave within the Serb area.
Mitrovica has been Kosovo's most volatile ethnic flashpoint, and the U.N. and NATO's effort to create peaceable coexistence between Serbs and ethnic Albanians there is seen as a test of whether a multi-ethnic Kosovo is possible.
"Some people say we're extreme because we want to protect ourselves. But the people who are in power are legalizing the displacement of Serbs," said Milan Ivanovic, a member of Mitrovica's Serb National Council.
The protesters, numbering around 5,000, cheered, whistled, chanted "Serbia!" and carried placards with slogans such as "Serbs have the right to live in Kosovo."
To the anger of ethnic Albanians, unofficial Serb guards known as "bridgewatchers" stop Albanains entering the north over the main bridge across the river.
The small "confidence zone" established last year and patrolled by peacekeeping troops and U.N. police, so far covers mostly Albanian areas in the south.
Extending the confidence zone, in which two-way radios and unauthorized people and vehicles are banned, would mean Serb leaders losing control of the north side of the bridge.
The Albanians complain the bridgewatchers are preventing members of Kosovo's ethnic Albanian majority from returning to their homes in northern Mitrovica that they fled in fear of Serb terror during NATO's 1999 bombing campaign.
But Serbs say the bridgewatchers are protecting Serbs from ethnic Albanian vengeance which has driven more than 150,000 Serbs across Kosovo from their homes since the end of the air war.
The killing of a 15-year-old ethnic Albanian by a grenade in the north of the town almost two weeks ago set off several days of clashes between Albanian protesters and French peacekeepers.
The clashes subsided only after a general declaration signed last week between Albanian leaders, Kosovo's U.N. governor Hans Haekkerup and Lieutenant General Carlo Cabigiosu, commander of the NATO-led KFOR peacekeeping force.
The document calls for increased police and peacekeeper presence on both sides of the river, an extension of the confidence zone and the return of displaced people to their homes, among other things.
Serbs at the rally demanded a separate Serb municipality in the northern part of Mitrovia, the removal of "confidence zones," and the return of Serbian security forces to Kosovo.
"A confidence zone is a zone of crime," said Ivanovic, who is also director of the local hospital.
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