Serbian voters cast ballots Sunday in a presidential election that will test the rule of strongman Prime Minister Aleksandar Vucic amid Russia’s growing influence in the Balkan area.

Vucic is expected to win the presidential election by a wide margin against 10 opposition candidates.

Vucic, a former ultranationalist who evolved into a self-declared pro-European politician, could be dealt a setback if he fails to sweep his opponents in the first round of voting.

The 47-year-old prime minister must win by more than 50 percent of the vote Sunday to avoid a runoff election on April 16.

Vucic’s main challengers for the presidency include human-rights lawyer and former Ombudsman Sasa Jankovic and former Foreign Minister Vuk Jeremic.

If Vucic wins the election, he is expected to transform the presidency from a ceremonial role into a more muscular position.

Although Vucic has said he wants to lead Serbia into the European Union, he has pursued closer relations with Russia, a longtime ally.

Just before the election, Vucic even visited Russian President Vladimir Putin, who reportedly promised to deliver warplanes, battle tanks an armored vehicles to Serbia.  The reports sparked concerns of an arms race in the western Balkans, a region Russia considers to be in its sphere of influence.