More than 400,000 Russians have been killed fighting in Ukraine since Moscow launched its full-scale invasion nearly five years ago, according to leaked data from the country’s state statistics agency, Rosstat.

The data, obtained by the Belarusian opposition-linked hacker group Cyber Partisans and the Ukrainian hacking collective Silent Crow, contains more than 11 million death certificates, including details of the deceased’s age, place of residence and location of death.

It was later shared with the Guardian and a small group of other outlets.

Of those, according to the groups’ data, 412,576 death certificates explicitly linked the fatalities to the war, either through official cause-of-death codes or written references to combat and military operations.

The figures underscore the staggering human toll of Russia’s nearly five-year invasion of Ukraine, with no end to the war in sight despite a fresh round of peace talks scheduled to take place in Abu Dhabi this week.

The two hacking groups announced the breach on 1 November and published the data over the weekend. Rosstat confirmed it had been hacked but denied that any sensitive information had been leaked.

The dataset offers an unprecedentedly detailed picture of Russia’s wartime losses, which Moscow has sought to conceal. The Russian authorities have not published a death toll since the early months of the invasion, and information about military casualties is treated as a state secret.

The Guardian could not independently verify the authenticity of the entire dataset. However, the figures are broadly consistent with other estimates of Russian losses. British intelligence in September previously estimated that about 500,000 Russian soldiers had been killed since the start of the invasion.

Separately, the independent Russian outlet Mediazona has identified by name nearly 286,000 Russian military personnel killed in Ukraine, drawing on official records, social media obituaries and photographs of gravestones. The outlet estimates that the true death toll is closer to half a million.

“The data looks authentic, and it’s very rich”, said Janis Kluge, the head of the Russia and Eurasia division at the German Institute for International and Security Affairs.

“This is the biggest leak of data when it comes to Russian casualties,” Kluge, who has extensively studied Russian war statistics, added.

The dataset is likely to underestimate the true death toll. Some soldiers remain missing, while others have never been identified.

Kluge also pointed to a significant delay between deaths occurring and being entered into official records, which he said typically amounted to about six months.

“We are probably at this time closer to 500,000 killed Russian soldiers than 400,000,” he said.

The figures reveal the starkly unequal burden of the war across Russia, with poorer and more remote regions suffering disproportionately heavy losses.

In Buryatia, Tuva and Zabaykalsky Krai, three regions in eastern Russia, war-related fatalities accounted for about a third of all deaths among men aged 18 to 49 between the start of the invasion and mid-2024. In Moscow and St Petersburg, the equivalent figure was about 10%.

The leaked data also points to a sharp rise in Russian battlefield deaths as the war dragged on, with some of the deadliest months coming in late 2024 and 2025.

Kluge, who has been analysing the data, said the number of soldiers killed in several months during that period exceeded 15,000, equivalent to roughly 500 deaths a day.

“In late 2024 and in 2025, you see that the numbers in many months are above 15,000 per month, and that’s higher than I think most estimates were,” Kluge said. “That’s 500 a day, above 500 a day. Certainly shocking.”

The scale of the losses is staggering by any measure and unprecedented in Russia’s modern history.

In less than five years, Russian military deaths in Ukraine are estimated to have exceeded the combined death toll from all Soviet and Russian wars between the end of the second world war and the start of the full-scale invasion in 2022 more than eightfold. The figure also exceeds the number of US military personnel who died during the second world war.

But rather than push Moscow towards a settlement, the scale of the losses is likely to harden Vladimir Putin’s resolve, according to a person familiar with the Russian president’s thinking.

“Putin understands these numbers, and for him to now settle for anything less than everything he wants would feel like a betrayal of himself and the people,” the person said.

Senior Russian and Ukrainian negotiators are due to meet in Abu Dhabi on Tuesday for the first US-brokered peace talks between the two countries in nine months.

Previous rounds of negotiations have made little progress towards ending the war, with talks stalling over Moscow’s demand that Ukraine withdraw from the parts of the Donbas region it still controls.

Neither Vladimir Putin nor Volodymyr Zelenskyy will attend the talks. Instead, both countries will send senior delegations, with Donald Trump’s envoys Steve Witkoff and Jared Kushner also expected to take part.

In a post on X, Witkoff said the negotiations would focus on “post-war security arrangement, de-escalation” and humanitarian issues.

European governments have expressed concern that the talks could extend beyond Ukraine to broader questions of European security, including Moscow’s longstanding demands for a reduction of Nato’s military presence in countries bordering Russia.

France’s foreign minister said Paris would participate in the negotiations but the Kremlin subsequently denied that France would be represented.