ISTANBUL, Turkey — Turks went to the polls Sunday in municipal elections seen as a key test for the embattled ruling party as a corruption scandal swirls around Prime Minister Recep Tayyip Erdogan and his inner circle.

The vote was widely viewed as a litmus test of damage done to the ruling Justice and Development Party, known by its Turkish initials AKP, by the graft probe and Erdogan’s increasingly authoritarian stance in the face of it.

The party handily won the last three general elections, but a poor performance in Sunday’s balloting could derail Erdogan’s presidential ambitions. That election is set to take place later this year.

“Turkey is a very centralized country, so local elections are never really about the municipalities — rather they are seen as a rehearsal for general elections,” said Cengiz Aktar, a senior scholar at the Istanbul Policy Center.

In the midst of the ever-expanding corruption investigation and a spate of leaked audios posted online over the past three months, Erdogan campaigned hard, casting the elections as part of a battle against sinister but unnamed foreign forces.

The prime minister’s rhetoric grew increasingly incendiary as the pressure on him mounted, often referring to opponents as traitors and “bloodsuckers.” In recent weeks, some pro- and anti-AKP rallies turned violent.

But despite Erdogan’s seeming missteps, including heavy-handed efforts this month to curb access to Twitter and YouTube, many Turks see little real alternative to the AKP. The prime minister drew large and supportive crowds on the campaign trail.

Sunday’s votes in Istanbul, the largest Turkish city, and the capital, Ankara, were the most closely watched. The southern cities of Adana and Antakya, which have borne the brunt of the exodus from neighboring Syria, were also seen as important in assessing public opinion on Turkey’s Syria policy.