BELGRADE, Serbia (AP) — Citizens of Belgrade are voting in a municipal election seen as a test of the ruling populists' firm grip on power in this Balkan country.

The election Sunday in the Serbian capital is for the local city authorities only but is considered important because of Belgrade's key role in the nation's economy and politics.

The governing center-right Serbian Progressive Party of President Aleksandar Vucic has led the polls ahead of the vote. But fractured opposition parties hope to mount a challenge in the traditionally liberal capital city.

They accused Vucic's party of intimidating opposition supporters, registering phony voters and slinging mud at political rivals in media outlets the party controls. The ruling party has rejected the accusations.

Some 1.6 million voters will choose the city assembly which appoints the mayor.