BELGRADE, May 11 (Reuters) - Serb nationalist leader Tomislav Nikolic on Sunday disputed a claim by pro-EU president Boris Tadic that his party would form the next government following Sunday's parliamentary election.

"There exist very clear possibilities of a coalition which does not include the Democratic Party (of Tadic)," Nikolic said in his first reaction to the election result, at the headquarters of his Radical Party.

He accused Tadic of a "grave violation of the constitution" by ruling out a coalition of nationalist parties, which collectively were close to a majority of seats in parliament although Tadic's party won most votes in the field of five.