Serbia intends to rule parts of Kosovo where loyal citizens still look to Belgrade for government, Prime Minister Vojislav Kostunica said on Monday.

In a fresh challenge to the West, which backs Kosovo's independence, and in particular to the European Union, which is due to take over from the United Nations as Kosovo's supervisor, he said Serbia would do all in its power to exert its authority.

Serbia will do everything to implement its jurisdiction and state prerogatives for all loyal citizens in Kosovo -- Serbs and non-Albanians, Kostunica said.

There cannot be normalization of relations with the states that recognized Kosovo independence until they annul their decision, he added. Protest rallies will not stop as long as illegal independence is not annulled.

Kostunica won renewed backing from ally Russia, whose likely next president, Dmitry Medvedev, made a high-profile visit to say Moscow would continue to back Serbian sovereignty, despite Western support for the independence of Kosovo.

Medvedev, who also met Western-leaning president Boris Tadic, said there would be no shift in Russia's support for Serbia after the presidential election next week.

We assume that Serbia is a single state whose jurisdiction covers all of its territory, Medvedev said. We will stick to this position.

Serbia cherishes Kosovo as the cradle of the nation, where Serb history and myth dates back 1,000 years and old monasteries dot the land. But most Serbs have little firsthand knowledge of the poor southern province, now populated by a 90 percent majority of ethnic Albanians.

Serbia and Russia insist that the 1999 United Nations Resolution 1244 is still the only valid international law on Kosovo. It made Kosovo a U.N. protectorate in 1999 under NATO-led peacekeeping but legally under Serbian sovereignty.

The United States said on Monday there was no going back from independence.

DON'T CONDONE VIOLENCE

We are going to continue to try to work with both the Russians and the Serbs on this but I think that it ought to be clear to everybody at this point that Kosovo is never going to be a part of Serbia again, State Department spokesman Tom Casey told reporters.

Tensions have risen in Kosovo's first full week as a separate state as Serbs vent their anger and determination to reverse the move.

In the Serb stronghold of north Mitrovica, over 1,000 people demonstrated for a seventh day, burning not only an EU flag but also a picture of Tadic.

Eighteen Kosovo police officers were injured when dozens of Serb war veterans lobbed stones and bottles during a protest at a border crossing into northeastern Kosovo. Police used teargas to disperse the demonstrators.

U.N. governor Joachim Ruecker urged Serbia to confirm its respect for the U.N. mandate, following Belgrade's endorsement of mob attacks on U.N.-run border posts and disruption of police and justice in the Serb-dominated north.

Ruecker said he reminded visiting Serb Minister for Kosovo Slobodan Samardzic that Resolution 1244 puts the United Nations and the KFOR peacekeeping force KFOR in charge of the whole territory of Kosovo.

I made it very clear to him that the condoning of violence, direct or indirect support for violence, is totally unacceptable, Ruecker said, referring to a remark by Samardzic saying that attacks on border posts were legitimate.

Samardzic said Serbia would do all it could to maintain peace and order in the areas that it controls, where Serbs live. Serbia would also provide jobs, schooling and infrastructure in Serb areas of Kosovo.

Europe's human rights watchdog meanwhile condemned what it called violent attacks on journalists covering Serb protests against the independence of Kosovo.

Hans Ola Urstad, mission chief for the Organisation for Security and Cooperation in Europe (OSCE), said in a statement that there had been direct threats against liberal Serb broadcaster B92 and other media and called for better protection of all national and international journalists.

Russia Dmitry Medvedev