Prime Minister Nikol Pashinyan on Monday pledged to build a new Armenia as he feted his victory after snap parliamentary polls following months of discontent over a humiliating military defeat to Azerbaijan.

Thousands of supporters, many with children, gathered on Monday evening in Yerevan's main square cheering the reformist leader and chanting his name.

Addressing his backers, Pashinyan, 46, insisted that the political crisis, which was sparked by Armenia's defeat to arch-foe Azerbaijan last year, was over and called for unity.

The embattled prime minister announced the gamble of snap polls earlier in the year, when protests against his rule were coming to a head The embattled prime minister announced the gamble of snap polls earlier in the year, when protests against his rule were coming to a head Photo: AFP / Karen MINASYAN

"Together we will build a new Armenia, our future and the future for our children," he said.

Analysts said many Armenians had cast their ballots for Pashinyan to prevent the return of old elites, a sentiment echoed on the streets of Yerevan.

Supporters at the rally praised Pashinyan's achievements over the past three years including freedom of speech.

"We support Pashinyan, we think he is an honest and good man," said 42-year-old doctor Karine Gevorkyan.

Armenia Prime Minister Nikol Pashinyan's party wins majority in snap polls Armenia Prime Minister Nikol Pashinyan's party wins majority in snap polls Photo: FACEBOOK / @NikolPachinyan / Ekaterina ANISIMOVA

Zarzand Aleksanyan, a 56-year-old teacher, also said his life had improved under Pashinyan. "They raised pensions and built roads," he said.

Pashinyan's Civil Contract party swept to victory with nearly 54 percent of Sunday's vote, overcoming anger at his handling of the devastating fight with Azerbaijan for control of the breakaway Nagorno-Karabakh region.

Armenia had to cede swathes of territory and the conflict claimed more than 6,500 lives on both sides.

Pashinyan's main rival Robert Kocharyan, whose alliance alleged foul play after receiving just 21 percent of the vote Pashinyan's main rival Robert Kocharyan, whose alliance alleged foul play after receiving just 21 percent of the vote Photo: AFP / Karen MINASYAN

Pashinyan's main rival Robert Kocharyan, who led Armenia between 1998 and 2008 and is seen as close to Russian President Vladimir Putin, said the vote was rigged but international observers gave it their thumbs up.

The prime minister took a gamble and announced snap polls when protests against his rule were coming to a head. He also claimed he had fended off a coup attempt from military leaders.

Armenia and Azerbaijan fought a vicious six-week war last year which claimed some 6,500 lives Armenia and Azerbaijan fought a vicious six-week war last year which claimed some 6,500 lives Photo: AFP / Karen MINASYAN

The Kremlin praised Pashinyan's "convincing victory", while EU Council President Charles Michel said the bloc was ready to support reforms in the country.

"We are also ready to further support regional stabilisation and comprehensive conflict settlement," Michel wrote on Twitter.

The calls from the opposition for Pashinyan's resignation began in November when he signed an unpopular peace deal mediated by Russia, an important military ally to Armenia, to end fighting with Azerbaijan.

Some in Yerevan, seen as a Kocharyan stronghold, expressed anger and disbelief on Monday.

OSCE election observers praised the polls as "competitive and well-run" and said that vote counting was "highly transparent OSCE election observers praised the polls as "competitive and well-run" and said that vote counting was "highly transparent" Photo: AFP / Karen MINASYAN

"We are in shock," Marat Muradyan, who fought in the Karabakh war with his two sons, told AFP. "We want to sell everything and leave."

Last year Armenia and Azerbaijan fought a vicious six-week war which saw Yerevan hand over swathes of territory in and around Karabakh to Azerbaijan.

Kocharyan, whose Armenia alliance received 21 percent of the vote, alleged foul play and vowed to take a complaint to the Constitutional Court.

"We have sufficient grounds to assert that the official election results do not represent a real balance of forces," his alliance said in a statement.

The alliance said it had "serious suspicions" that the election results were tampered with, citing power outages in several regions during vote counting.

Kocharyan's grouping was set to address reporters on Tuesday.

The vote was followed by Armenia's Soviet-era master Russia, long-standing rival Azerbaijan and its ally Turkey, a key backer of Baku in the Karabakh war.

Observers from the Organisation for Security and Co-operation in Europe however praised the polls as "competitive and well-run" and said that vote counting was "highly transparent."

"The fundamental freedoms key to democratic elections were generally respected," OSCE monitors said.

Kocharyan was himself accused of rigging a presidential election in favour of an ally and presiding over a deadly crackdown on protesters in 2008.

In 2018, Armenia won international praise for holding the country's first free and fair vote under Pashinyan.

OSCE observers did however point to "intense polarisation" in Armenia's political landscape, saying the race was "marred by increasingly inflammatory language from key contestants".

The candidates exchanged insults and threats during the campaign. Pashinyan brandished a hammer at rallies, while Kocharyan, 66, said he was ready to fight the prime minister in a duel.