Top U.S. and Russian envoys toured Balkan capitals Tuesday in an effort to defuse tensions in Serb-ruled Kosovo, while Serb police said one of their officers had been injured in another attack in the troubled province.

Serb officials said the policeman sustained slight injuries in a grenade attack late Monday near Pec, 30 miles west of Kosovo's capital, Pristina. No other details were released, and the report by Serbia's state-run Tanjug news agency could not be independently confirmed.A clandestine ethnic Albanian militant group shot dead four policemen Feb. 28, prompting a police crackdown in which at least 80 ethnic Albanians were killed. The police sweep generated international condemnation, and world leaders are considering what measures to take to avoid another Balkan war.

The two sides are clinging to their positions - ethnic Albanians, with a 9-to-1 population majority, insisting on independence, and the Serbs refusing to allow Kosovo to secede, although they have offered talks that could lead to a restoration of Kosovo's autonomy.

For the fourth time in six days today, leaders of Kosovo Albanians boycotted proposed talks with Serb officials in Pristina. The Albanians demand the presence of foreign mediators at any talks with the Serbs.

After talks in Belgrade today with Russian Foreign Minister Yevgeny Primakov, Yugoslav Foreign Minister Zivadin Jovanovic dismissed "pressures" for foreign mediation and reiterated his government's stance that "Kosovo is an internal Serbian matter."

The Russian foreign minister also is to meet with the Balkans' chief power broker, Yugoslav President Slobodan Milosevic. Serbia is the largest of two republics in the Yugoslav federation.

Primakov said Russia, a traditional Serb ally, supports Kosovo remaining part of Serbia. He also urged "a wider right of self-rule" for Kosovo Albanians.

Deputy Secretary of State Strobe Talbott visited Macedonia, which borders Serbia and also has a large restive ethnic Albanian minority.

He urged that international troops stick to their posts on Macedonia's border to keep any violence in Kosovo from spilling over. About 1,000 military observers, more than 300 of them American and the remainder from Scandinavian countries, currently are deployed in Macedonia.