BELGRADE, Serbia (AP) — Chanting "Thieves! Thieves!," thousands of opposition supporters protested Saturday in front of Serbia's state electoral commission over what their leaders said was widespread vote rigging by the ruling populists.

The center-right Serbian Progressive Party of Prime Minister Aleksandar Vucic won last weekend's general election by a landslide, but has demanded a vote recount after several smaller opposition parties won seats in Parliament.

The Progressives won 48 percent of the seats in the 250-seat Parliament, but that is 27 seats fewer than in the previous vote in 2014.

The ruling party complaint led to the annulment of votes from several polling stations and the failure of one nationalist party, DSS-Dveri, to pass the 5 percent threshold to enter Parliament by the slightest margin — one vote. That would mean that the ruling Progressives would add seven more parliamentary seats to their tally.

In a rare show of unity, opposition party leaders addressed the protesters Saturday, claiming numerous irregularities during the vote, including intimidation and the bribing of voters.

"We gathered here today to defend freedom. To defend justice. To defend free Serbia. To defend the will of the Serbian people so Serbia doesn't become, step by step, another North Korea," said Sandra Raskovic Ivic, a leader of the DSS-Dveri coalition. "We will not let that happen."

Vucic called the vote two years early, saying he wanted a clear, new mandate to steer Serbia further toward European Union membership. Critics say Vucic's real intention was to consolidate his authoritarian rule while his popularity was still high.