Moscow has criticised Latvia for rejecting Russian as a second language in a highly emotive referendum that exposed the tensions lingering in the Baltic nation since its years under Soviet rule.
The Russian foreign ministry said on Sunday the referendum's outcome was biased because it excluded so many Russian-speaking "non-citizens" from the vote.
"The referendum's results far from fully reflect national sentiments because 319,000 'non-citizens' were denied the right to express their opinion, even though many of them were born in Latvia or have lived there a long time," the ministry said.
"We hope that the voice of Latvia's Russian population will be heard by both the ruling government and international organisations whose job it is to make sure that basic laws protecting the legal rights and interests of minorities are followed," it said.
The statement also expressed "bewilderment" that Latvia's election authorities did not grant a team from Russia's Kremlin-run Public Chamber the status of official referendum observer.
The official referendum results mirror an ethnic split in a 2011 census that shows Russians making up 27 per cent of Lavia's two million-strong population. About one-third of the country's 2.1 million people consider Russian as their mother tongue.
That census identified some 290,000 Latvian "non-citizens", a figure that could have theoretically doubled the vote in favour of Russian language, although that would not have changed the overall result.
The Russian-minority sponsored motion was headed for almost certain defeat even before Latvian leaders hailed results showing a 75 per cent "no" vote as proof of their country's formal break with its past.
"An overwhelming majority of Latvian citizens have expressed their unequivocal support for one of the core constitutional values, the national language," Andris Berzins, the Latvian president, said in a statement.
The three Baltic states remained the most unruly members of the Soviet Union after their World War II annexation and often flaunted their suspicions of Russian settlers in the subsequent decades.
An independent Latvia emerged from the Soviet Bloc in 1991 and quickly adopted some of the strictest language rules of all the former Soviet-run nations.
Hundreds of thousands of Russians, many of them living in the capital Riga, ended up failing those exams and became deprived of the jobs and other social privileges that accompany Latvian citizenship.
Many consider Russian the language of the former occupiers.
Some officials in Latvia sounded a more conciliatory note after the outcome amid signs of a new citizenship referendum being organised by the same Russian minority in the months to come.
"Your votes show we need to do a lot of homework in order to help a significant proportion of the population feel that the Latvian state and its core values are their own," Edgars Rinkevics, Latvia's foreign minister, told the losing Russian voters.
"Many feel alienated, and for them it was a protest vote," Rinkevics said in a statement.
Russian-language activist Vladimirs Lindermans told Latvian television he felt vindicated by the referendum.
"Now we will see if people are ready to open dialogue with the Russian community. We have shown that Russian is not a foreign language here," the Native Tongue group leader said.
Latvia formally joined the European Union in 2004 and has largely avoided criticism from Brussels for its language policy despite Moscow's complaints.