The Organisation for Security and Cooperation in Europe said there had been abuses in the election including vote-buying, putting pressure on public servants, and intimidating of voters to vote for certain parties.
President Serzh Sarksyan's ruling Republican Party won elections in Armenia on Sunday, official results showed on Monday.
The vote will lay the foundation for a new parliamentary system of government.
The Republican Party of Armenia (RPA) had 49.12 percent of the votes while the opposition Tsarukyan Alliance led by wealthy businessman Gagik Tsarukyan gathered 27.32 percent.
The government-loyal Dashnaktsutyun Party had 6.57 percent and the opposition bloc Yelk ("Way Out") 7.77 percent, enough for both to enter parliament.
Central Election Commission chairman Tigran Mukuchyan said the figures were based on results from all 2,009 polling stations.
He said nothing about violations of election rules.
But the prosecutor's office said it had been reviewing media reports of violations during the voting and count process.
Opposition parties said they had also filed complaints on irregularities to the prosecutor's office, but gave no further details.
The Organisation for Security and Cooperation in Europe, observing the conduct of the election, said on Monday there had been some abuses.
It said in a statement the poll was "well administered and fundamental freedoms were generally respected", but added: "There was credible information of vote-buying, of pressure on public servants including in schools and hospitals, and of intimidation of voters to vote for certain parties."