Nine French peacekeepers were injured by a grenade blast Thursday night as they repelled an ethnic Albanian mob assaulting a Serbian demonstration in this divided Kosovo city, NATO officials said today.

The clash occurred as human rights observers reported increasingly perilous living conditions for non-Albanians in the Serbian province.

The grenade attack took place in the middle of a Serbian-Albanian confrontation that featured gunfire and stone-throwing. Dozens of Albanians tried to ford the shallow Ibar River and move into the northern, largely Serbian part of the city. The Serbs have blocked the bridge over the Ibar since July, suspecting that the Albanians plan to overrun their neighborhoods.

Mitrovica has become a prominent exhibit in the bitter ethnic conflict that has continued in Kosovo since the end of the war. Thousands of Serbs have fled the province since June, when Yugoslav army and Serbian police forces withdrew and NATO-led peacekeepers began arriving along with hundreds of thousands of ethnic Albanians who had been forced into exile during the war. Some Albanians have taken revenge for their brutal ouster by burning Serbian houses and assaulting Serbian civilians.

The French injuries, all of them minor, were the worst single-day total suffered by the peacekeeping operation. A French spokesman, Capt. Bernard Bonneau, said that although the grenade appeared to have been thrown from the river area, darkness made it impossible to say exactly who had hurled it. Both Serbs and ethnic Albanians were wounded in the melee, mostly by rocks but also by gunfire. The peacekeepers shot bullets and tear gas to disperse the crowds.

Ethnic Albanians complained that the French fired exclusively on them and were taking the Serbian side in the long-running standoff in the city, which is about 20 miles northwest of Pristina, the Kosovo capital.

"The French are keeping the city divided. We are refugees in our own country," said Senad Zatriqi, a merchant who sported a gash on his forehead. He said he was knocked unconscious by a stone as he tried to cross the river "to visit my house," where he had lived before the war.

This evening, Albanians again tried to cross the Ibar, but the French turned them back. Masked ethnic Albanian youths hurled rocks, and gunshots were heard on both sides of the river. "The Albanians are on the offensive today," Bonneau said.

Today's human rights report, meanwhile, underscored the difficulties facing the West as it seeks to preserve a multi-ethnic Kosovo, which nominally remains a province of Serbia, Yugoslavia's dominant republic.

The report said non-Albanians continue to flee Kosovo, largely out of fear, although it said exclusion from medical care, education and jobs--now controlled by the province's ethnic Albanian majority--is a factor. About 97,000 Serbs remain, compared with a prewar population of about 200,000. The size of other minority groups, including Turks and Gypsies, has shrunk as well.

"People want to leave because they feel there is no future for them here," said Sandra Mitchell, a representative of the Organization for Security and Cooperation in Europe, which issued the report jointly with the United Nations.

A growing number of enclaves exclusively populated by Serbs or other minorities are "becoming prone to attack" despite being under NATO protection, the report said. In the few remaining mixed hamlets where ethnic Albanians are a minority and Serbs the majority, the Albanians also "face insecurity."

Inter-ethnic clashes have intensified in the past week, especially in eastern Kosovo, which is under the control of U.S. forces. Mortar attacks, drive-by shootings, beatings and other violence are nearly daily occurrences.

A U.S. military analyst blamed both Serbs and ethnic Albanians for creating unrest for political reasons: Both sides want to build pressure for the introduction of their own security forces.