Voters in Kyrgyzstan have given clear approval to a new constitution giving parliament more power, officials say.
With nearly all the votes counted, the election commission said 90% of voters were in favour of the plan to limit the president's powers.
Russian President Dmitry Medvedev said he feared the move could fuel extremism.
The interim government called the referendum after President Kurmanbek Bakiyev was overthrown in April.
The referendum took place about two weeks after a wave of clashes between ethnic Kyrgyz and Uzbeks in the south, when hundreds of people were killed.
Opposition parties had called the timing of the referendum inappropriate.
'Strong authority needed'
With ballots from 90% of all precincts counted, the Central Election Commission said more than 90.7% of those who voted supported the new constitution and nearly 8% voted against it.
Some 2.7 million people were eligible to vote, and turnout was nearly 70%, it said.
Interim leader Roza Otunbayeva endorsed the outcome in comments shortly after polls closed.
She called the vote historic, saying the Central Asian nation was now on the path "to a true government of the people".
The referendum was supported by the UN, the US and Russia, as a step towards restoring democracy.
A US State Department spokesman welcomed the orderly vote and said the US hoped it constituted "an effective step towards stable, democratic governance".
But speaking to reporters at the G20 summit in Canada, Mr Medvedev said adopting a parliamentary constitution could fuel extremism in Kyrgyzstan.
"I have a hard time imagining that a parliamentary republic could work in Kyrgyzstan, that it won't provoke a series of problems and encourage the rise to power of extremist forces," he said.
"Kyrgyzstan is confronted by many problems, notably the threat of breaking up. To avoid this you need a strong, well-organised authority."
Kyrgyzstan was part of the Soviet Union before its independence in 1991. Both the US and Russia have military bases in the country.
The BBC's Tom Esslemont in the capital, Bishkek, said the conditions for holding a referendum were far from perfect.
Health officials say 275 people were killed in ethnic clashes in the south earlier in June, but other officials put the number of deaths at 2,000.
Thousands of homes and businesses were destroyed and an estimated 400,000 people - many of them from the minority ethnic Uzbek community - were displaced.
The violence has abated but the country's Uzbek and Kyrgyz populations remain deeply divided.
Observers in the south said voters had turned out from all ethnic communities.
Dinara Oshurakhunova, a pro-democracy activist monitoring the vote, told the Associated Press news agency that people many people did not understand what they were voting for.
"For them, taking part is simply an opportunity to stabilise the situation," she said.
Interim President Roza Otunbayeva said she now would be inaugurated as a caretaker president and form a government.
Parliamentary elections are to be held in October and Ms Otunbayeva will remain president until the end of 2011, when she is to step aside.
Parliamentary elections would be held every five years and the president limited to a single six-year term.
But opposition parties and some human rights groups have criticised the vote, saying it is happening too soon after the ethnic clashes in Osh and neighbouring Jalalabad.