Tadic was speaking in a broadcast address on the fourth anniversary of the fall of the Slobodan Milosevic regime.
Tadic called on the Kosovo Serbs to go to the polls, but added that he would demand that Serb deputies leave the provincial assembly unless the conditions set were met 90 days from the day of inauguration of the Kosovo interim government. He also urged the Serbian government to make it possible for all displaced persons to exercise their voting rights in accordance with the law.
He noted that Serbian Prime Minister Vojislav Kostunica, many political parties and organisations of the Kosovo Serbs, and the head of the Serbian Orthodox Church, Patriarch Pavle, had been against the Serbs participating in the Kosovo elections.
Tadic pointed out that Belgrade wanted a minimum of local Serb government to be established in Kosovo, saying that the Serbs should have control of the police, judiciary, health services and education in areas where they are in a majority.
The president said that it was necessary to take a firm position in negotiations on the final status of Kosovo and that this required the participation of Serbs in the elections.
Speaking of war crimes indictees, Tadic said: "It is in our national interests that the State should help them in establishing the truth. That's why the Government of Serbia must abide by the law. The executive authority cannot freely interpret decisions by the judiciary. Politicians cannot downplay court decisions by leaving their implementation to the free will of those indicted." He called on the government to fulfil its legal obligations or take the consequences.
The speech received divided responses from Kosovo leaders.
Kosovo Premier Bajram Rexhepi described the speech as unacceptable and rejected the demand for control of the police, the judiciary and education in the Serb-majority areas, saying that it represented an attempt to legalise the existing parallel government structure of Serbs in Kosovo.
Rexhepi said that Serb citizens of Kosovo should think and decide for themselves rather than wait for suggestions from Belgrade.
One of the Serb leaders in Kosovo, Oliver Ivanovic, told Serb media in Pristina that he supported Tadic's speech.