The Kremlin has gone to great lengths to deny any direct involvement in the war in Ukraine, even as Russian soldiers have entered eastern Ukraine in increasing numbers since April to fight alongside pro-Moscow separatists.

But despite tactics ranging from blunt official denials to government pressure on soldiers’ families to remain silent, there is mounting evidence that Russian soldiers are not just fighting in Ukraine.

They are dying there in large numbers.

Observers from the Organization for Security and Cooperation in Europe said they watched a cargo vehicle cross the border on Nov. 4 near Donetsk as it headed back to Russia. The vehicle was among the troop movements and military vehicle crossings OSCE chronicled in a weekly report.

The vehicle had the marking Груз 200, or Gruz 200—Russian for “Cargo 200,” which is a well-known Russian military designation for the bodies of soldiers killed in action.

In addition, Ukrainian government officials said their security personnel sighted five cargo vehicles with Gruz 200 markings leaving Ukraine for Russia on Nov. 11.

The Kremlin has steadfastly denied that Russian troops are in Ukraine. To explain away eyewitness reports, photographs and videos of Russian troops in the embattled country, Russian authorities have claimed that soldiers were volunteers on holiday … or had become lost during maneuvers.

“I tell you completely openly and officially that there are no military movements across the border and moreover none of our military personnel have been or are present on the territory of southeast Ukraine,” Alexander Lukashevich, a Russian foreign ministry spokesman, said during a media briefing on Nov. 13.

In its mid-November report, OSCE said that it observed 630 people in military clothing crossing the checkpoint near Donetsk during the weeklong reporting period, most of them bound for Ukraine.

In past conflicts such as the Soviet war in Afghanistan during the 1980s, the Kremlin was tight-lipped about casualty figures. The secrecy left many Russians without any information about how or where their sons in the Red Army died. This obfuscation contributed to the mounting disillusionment with a war some have called “Moscow’s Vietnam.”

Above—the grave of a Russian soldier who died on Aug. 18 in Ukraine. He is buried in the Krestovsky Cemetery in Pskov. Photo via Gruz-200 Facebook page. At top—in June, independent journalist Tatyana Turchenkova photographed one of the Gruz 200 trucks nearing the Ukraine-Russia border. Photo via Gruz-200 Facebook page

Now, some Russians worry that history is repeating itself in Ukraine. Families receive a soldier’s body for burial with information about the date of death, but nothing more — and the Russian government responds to questions by threatening to cut off death benefits or send family members to prison for national security violations.

To penetrate the official wall of silence, self-described human rights activist Elena Vasilieva, a Russian, started the Facebook group Gruz-200, which allows friends and family of soldiers in Ukraine to exchange information.

Some use the Facebook page—which has 28,000 members—to help determine the circumstances surrounding the combat deaths of their loved ones. Many claim to have military sources confirming the use of the Gruz 200 trucks to quietly transport dead Russians.

Vasilieva estimated that as many as 4,000 Russians have died in Ukraine, based on information she has obtained from her Facebook group.

“We don’t know the number of wounded and those who could die of wounds, as this figure is hidden,” Vasilieva said during a media briefing in Kiev on Sept. 26.

She said not all the bodies of Russians killed in the eight-month war get shipped back to Russia. Vasilieva alleged that the Russian government secretly buries many of the dead soldiers in mass graves.

Vasilieva’s death toll figure could be too high. But to be fair, no one really knows for sure how many people have died in Ukraine—on either side of the conflict.

In early September, the U.N. estimated at least 3,000 people had perished since April, an increase of no fewer than 800 in just one week. “The actual number may be significantly higher,” said Ivan Šimonović, the U.N.’s assistant secretary-general for human rights.

During a Nov. 15 interview with the Russian language publication Gordonua, Vasilieva said she traveled through Ukraine in September to shoot a documentary with her iPad that she calls Ukraine: In Search of the Truth.

Vasilieva said she made the video because she “promised to provide parents of Russian soldiers with incontestable proof of the participation of their children in the war in Donbass.”

“Officers write that the war will end in a month, not later, because Putin will run out of soldiers soon,” Vasilieva said. “They will be replaced with conscripts, and these are inexperienced boys who can either be killed at once or be taken prisoner.”

Seemingly unfazed by its losses, Moscow appears ready to launch a winter offensive that could intensify fighting in Ukraine.