Ivica Dacic, the leader of the Socialists, said he was under similar pressure four years ago when Washington urged him to join a coalition with the Democrats.
"What do you think there are no pressures from the other side?" Dacic, late Serbian autocrat Slobodan Milosevic's wartime spokesman, asked reporters. "Four years ago, representatives of Western governments called me to support the Democratic Party government, and no one was worried about that at the time."
Dacic, who made a surprise visit to Russia last week, said he will not succumb to pressure from either Washington or Moscow when he decides with whom he'll form the next government.
Neither the Democrats nor the nationalist Serbian Progressive Party won enough votes in Serbia's parliamentary elections in May to rule alone and are trying to lure the Socialists to form a coalition government, which the EU hopes will continue in its bid to become a member of the bloc.
Russia does not openly oppose Serbia's EU candidacy. But Kremlin officials have repeatedly warned that when Serbia becomes a member of the bloc, it would hurt traditional ties between the two Slavic nations, and would downgrade mutual trade relations.
Democratic Party leader Boris Tadic, who lost the presidential election to nationalist leader Tomislav Nikolic, held a series of negotiations with Dacic on the forming of the new government, but without apparent success.
Tadic said Thursday that the formation of the government is "a difficult process," and in an apparent reference to Dacic, he said "people should be ready for a compromise."
Dacic said that if the talks with the democrats fail, he will negotiate with the nationalists. They are reportedly offering Dacic the chance to become the prime minister, something he would not get in a government led by Tadic.
The Progressives, who claim to have shifted from being staunchly anti-Western to pro-EU, on Thursday urged Dacic to start coalition negotiations with them, saying his talks with the Democrats "have obviously failed."