Russia on Saturday more than doubled its official coronavirus death toll for April to 2,712 after changing how it classifies fatalities.
Officials warned that May's death toll was likely to be even worse in Russia, which has the world's third largest number of cases with 520,129.
The country reported 8,706 new cases on Saturday after its number of new infections peaked in mid-May.
The capital Moscow — the nation's worst affected city — lifted tight lockdown measures last week.
Russia's death toll has been much lower than in other countries with large outbreaks, raising questions over possible underreporting of deaths.
The April figures from Rosstat, the official statistics agency, include 1,270 deaths where the virus was the main cause.
But they now also include deaths where the victim tested positive for the virus but it was not the main cause of death.
In April there were 435 deaths where the virus had a "significant influence" and 617 where it was present but did not play a major role, the agency said.
The statistics also include 390 cases where the person initially tested negative to coronavirus, but it was later ruled to be the main cause of death.
The previously announced toll for April was 1,152.
Russia has previously made public a total death figure of 6,829 for the pandemic, a preliminary figure based on daily counts.
Officials including First Deputy Prime Minister Tatiana Golikova have said the change in the way deaths are counted follows recommendations of the World Health Organization.
Russia had previously attributed its low death figures to mass testing and its practice of carrying out autopsies to establish cause of death.
The new April figure represents a death rate of 2.6 percent among those infected, Golikova said at a televised briefing on Saturday.
The death rate for May will be higher, she added.
"The main blow will fall in May and probably the first half of June," she said.
"Doctors are now fighting for citizens' lives, especially those who are on ventilators."
On Wednesday, the health department in Moscow reported that 5,260 people had died in May, using the new method of classifying virus deaths -- a death rate of 3.8 percent.
Official death statistics for May are not yet available for the whole country.
The state statistics agency had delayed its release of death figures for April, the first full month of Russia's outbreak.
Golikova said earlier that this was because regional laboratories were still processing autopsy results.