Election authorities reported on October 7 that two populist parties seen as potential Harmony partners, KPV LV and the New Conservative Party, polled 14.1 percent and 13.6 percent, respectively.
"This is breaking our agreement with North Atlantic Treaty Organisation, of which Latvia is a member since 2004, he adds".
Along with fellow Baltic states Estonia and Lithuania, Latvia declared independence in 1918 after the Tsarist Russian empire collapsed.
Before the election, some Latvians were concerned that a strong result for Harmony and the populist KPV could lead to their forming a government and bringing Latvia's foreign policy closer to Putin's Russian Federation.
A pro-Russia party looks to have won the most votes in Latvia following Saturday's general election.
The center-left Socialist party, commonly known as Harmony, received almost 20 percent of the vote after ballots from 575 polling stations were counted.
Members of the Russian minority account for about 25 percent of Latvia's almost 2 million people, a legacy of almost 50 years of Soviet occupation that ended in 1991.
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"Voters want new faces: the current ministers can not offer anything entertaining", political scientist Filips Rajevskis told AFP. Together with Latvia's more established nationalist party, the National Alliance, which came in 5th place, nationalist-populist parties received over 25% of the overall vote. "That's where the populism kicks in", he said.
More than 1,000 North Atlantic Treaty Organisation troops are based in the Baltic country and even the potential of a minor shift in allegiance in Latvia has set alarm bills ringing in Brussels and Washington.
The ethnic divide is strong in Latvian politics and other parties have always shut Harmony out of government.
Including both the Greens and Farmers, and New Unity would create a more comfortable 61-seat majority, but a five-party coalition would be harder for a prime minister to control.
A corruption scandal has undermined voters' confidence in the government.
Ethnic Latvian parties have resolutely kept the pro-Russia Harmony party from power in the former Soviet republic as they sought ever closer ties with the West.
Latvia, a member of the European Union and North Atlantic Treaty Organisation, shares a 276-kilometre (167 miles) border with Russian Federation. "We don't have any red lines regarding any other political force", lawyer Aldis Gobzems, KPV LV's candidate for prime minister, said in a recent TV debate. Polling stations open on Saturday from 0500 GMT to 1700 GMT, with exit polls soon after and results expected early Sunday.