BELGRADE — Opponents of Serbia's populist President Aleksandar Vucic took to the streets claiming the weekend's snap elections were rigged as international observers said on Monday the vote was held in “unjust conditions" with multiple reports of irregularities.

Political tensions have spiked in the Balkan country over the parliamentary and local elections on Sunday.

In Belgrade, several thousand people gathered in front of the state election commission headquarters, chanting “thieves,” as opposition leaders moved to lodge formal complaints claiming fraud in the city election.

"We should not be silent about this," said student Danica Samardzic who took part in the demonstrations.

"This protest is just the beginning of something bigger, so we can achieve the goals that made us come out here."

“We have hundreds and hundreds of complaints," said opposition politician Marinika Tepic.

She and several other opposition politicians would camp inside the building that's the seat of the state election commission.

Vucic's ruling Serbian Progressive Party won the parliamentary vote, an early official count confirmed.

However, in the Belgrade local election, an opposition group said it was robbed, would not recognize the results and would demand a rerun of the ballot.

The Serbian president appeared on state RTS television on Monday evening, stating that the “election was fair” and that he wanted "to tell the people not to worry ... peace, law and order will prevail.”

In a preliminary statement, a mission made up of representatives of international rights watchdogs said the vote was “marred by harsh rhetoric, bias in the media, pressure on public sector employees and misuse of public resources.”

“Election day was smoothly conducted, but was marked by numerous procedural deficiencies, including inconsistent application of safeguards during voting and counting, frequent instances of overcrowding, breaches in secrecy of the vote, and numerous instances of group voting,” the conclusions said.

Vucic, who has been in power since 2012, has dismissed criticism from his opponents that his government curbed democratic freedoms while allowing corruption and organized crime to run rampant.

Under Vucic, Serbia became a candidate for EU membership, but the opposition accuses the bloc of turning a blind eye to the country's democratic shortcomings in return for stability in the Balkan region, still troubled after the wars of the 1990s.

The election pitted Vucic's SNS against the Serbia Against Violence opposition alliance, or SPN.

Vucic's party won nearly 47 per cent of the ballots in the parliamentary vote, followed by Serbia Against Violence with 23 per cent, according to a near-complete preliminary tally by the state election commission.

Several other smaller parties also competed in the election, which was held only 18 months after the previous presidential and parliamentary vote.

If confirmed in the final vote count, the result means that the SNS party will have an absolute majority in the 250-member parliament and will form the next government on its own.

Official results for the city hall in Belgrade are yet to be announced, but projections by polling agencies IPSOS and CESID said SNS won 38 per cent of the ballots, while Serbia Against Violence garnered 35 per cent.

Irregularities also were reported by election monitors and independent media in Serbia. — Euronews