By Thomas Grove and Maria Tsvetkova

MOSCOW 2014 (Reuters) - Late last month Yelena Tumanova was handed the body of her son in a coffin at her home in Russia's Western Volga region. Anton Tumanov was 20 and a soldier serving in the Russian army in the North Caucasus region of Chechnya.

The documents Yelena Tumanova was given with the body raised more questions than they answered - questions about how her son died and about the Russian government’s denials that its troops are in Ukraine. The records do not show Anton Tumanov’s place of death, said human rights activists who spoke to his mother after she got in touch with them.

"Medical documents said there were shrapnel wounds, that is he died from a loss of blood, but how it happened and where were not indicated,” said Sergei Krivenko, who heads a commission on military affairs on Russia’s presidential human rights council.

Yelena Tumanova could not be reached for comment and Reuters was unable to review the documents. But more than 10 soldiers in her dead son’s unit told Krivenko and Ella Polyakova, another member of the presidential human rights council, that Anton Tumanov died in an Aug. 13 battle near the Ukrainian town of Snizhnye. The battle, the soldiers said, killed more than 100 Russian soldiers serving in the 18th motorized rifle brigade of military unit 27777, which is based outside the Chechen capital of Grozny.

Rolan, 23, a fellow soldier who served with Tumanov, told Reuters that his comrade died on the operating table after he was hit by shrapnel from rockets. Rolan said he was steps away in an armored personnel carrier when the rockets struck. He said two in his group died, including another soldier, named Robert.

"I was inside an APC, hatches were open, and as a result I was lightly stunned and shell-shocked," said Rolan.

"Robert and Anton were outside two or three steps away and they simply did not manage to hide. Robert died right there. We gave first aid to Anton, he was already on the operating table when he died," said Rolan, now at home in Russia's Krasnodar region where he is recovering from an injury.

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Human rights workers and military workers say some 15 other Russian soldiers have been killed in Ukraine, with hundreds more now in hospital.

The fact that Russian soldiers have died in a war in which they officially have no involvement is a problem in Russia. Chatter about young soldiers returning home in coffins has begun to spread over the past few weeks. Though still limited, such talk has powerful echoes of earlier Russian wars such as Chechnya and Afghanistan.

Ukrainian President Petro Poroshenko said this week that Russia had moved most of its forces back across the border into Russian territory after a ceasefire between Kiev and the separatists in Donetsk and Luhansk provinces. But a NATO military officer said on Thursday that Russia still had 1,000 troops in the country.

The idea of an outright invasion of eastern Ukraine by Russian troops is highly unpopular in Russia. A survey by pro-Kremlin pollster Fund of Social Opinions said 57 percent of Russians support the separatist Donetsk and Luhansk People's Republics, but only 5 percent support an invasion of Ukrainian territory.

Russian authorities have worked to systematically silence rights workers' complaints over soldiers’ deaths, intimidating those who question the Kremlin's denials that its soldiers are in Ukraine.

Krivenko and Polyakova, who is also the head of an organization representing soldiers' mothers in St. Petersburg, filed a petition on Aug. 25 asking Russian investigators for an explanation for the deaths at Snizhnye.

So far they have heard nothing. But soon after the petition was filed to the Investigative Committee, a law enforcement body that answers only to President Vladimir Putin, Polyakova was told her organization, which has existed since the 1991 break-up of the Soviet Union, had been branded a 'foreign agent.'

The term, brought in by Putin in 2012 to set apart non-governmental organizations that receive foreign funding and engage in political activities, carries no real punitive measures but is often used to discredit critics of the Kremlin.

Polyakova says she has been at odds with the authorities over her stance toward Russia's annexation of Crimea. She believes authorities gave her the ‘foreign agent’ tag because of her petition and an Aug. 28 interview with Reuters in which she first accused Moscow of covering up the deaths of Russian soldiers.

"It's all linked. This was just the last drop, so to speak," she said.

SERVING IN UKRAINE

Officially there have been no Russian soldiers in Ukraine. But Kiev maintains that Russian troops have in the past few weeks helped separatists reverse the tide of the conflict, pushing Ukrainian forces back from the Russian border and allowing the separatists access to the sea.

And Reuters was able to find people who know of hundreds of soldiers injured in Ukraine, or whose relatives are fighting in Ukraine, building up the most comprehensive picture yet of Russian battlefield casualties in the country.

A military doctor told Reuters that hundreds of Russian soldiers injured in fighting in eastern Ukraine are now in military hospitals in the regions of Moscow, St. Petersburg and Rostov, which borders Ukraine.

"Generally they bring (the injured) to Rostov and to Moscow," he said.

Sergei Kozlov, an IT specialist in Moscow, says his nephew Nikolai, a paratrooper based in Ulianovsk, was sent to Ukraine on Aug. 24. He was hit by a shell after he crossed the border, Sergei Kozlov said, and lost his leg.

"He was operated on in Rostov Province and then was brought to Moscow because there was no more room there. But even now there is no room in Moscow hospitals or in St. Petersburg because they're all filled with people injured in Ukraine," Sergei Kozlov said by phone. Nikolai, who Sergei said is still in hospital, could not be reached.

A cab driver in Moscow who gave his name as Vitaly said his son was also sent to Ukraine. He has a picture on his dashboard of the 20-year-old boy smiling atop an armored personnel carrier.

Vitaly says he is furious that his son – a paratrooper based in Pskov near Estonia - has been sent to Ukraine to fight for the rebels.

"They sent him there illegally to fight for the rebels two weeks ago. He says he'll be back on Nov. 20. I'm counting the days," he said.

Vitaly says officers tried to force his son - serving mandatory military service - to change his status to a contract soldier, which would legally allow him to serve abroad. Conscripts in Russia are exempt from foreign service.

His son refused to sign, but officers sent him to Ukraine anyway.

"They dressed him up like a rebel so no one would know he was a Russian soldier and off he went," said Vitaly.

Rolan, the serviceman who fought alongside Tumanov in Snizhnye, says he spent 10 days fighting in Ukraine in the middle of August. Back home in the Krasnodar region, he said his commanders offered soldiers the option to go to Ukraine. The men could refuse, but the commanders were very supportive of those who agreed. Rolan went, he said, because of his military oath and to protect Russian-speakers from Ukrainian forces, routinely referred to as fascists, in Russia. His unit put him on paid leave to make the trip.

"(I wanted) to push neo-Nazis and pure fascists deep into the country or eliminate them and to free Russian-speaking population of this evil," he said.

He said he crossed into Ukraine in a truck without a license plate.

"On the Ukrainian side of the border, rebels met and guided us. In fact there is no border, just a field of sunflowers. There is Russia on one side of it and on the other side there is no more Russia."

“NO RELATION TO REALITY”

Independent Russian news outlet Dozhd has tried to keep a list of the Russian soldiers injured, detained or killed in Ukraine.

But the number of Russian soldiers serving on the side of pro-Russian rebels against Ukrainian troops is unknown.

Russia's defense ministry strongly denied reports that Russian military units were operating in Ukraine.

"We have noticed the launch of this informational 'canard' and are obliged to disappoint its overseas authors and their few apologists in Russia," a ministry official, General-Major Igor Konashenkov, told Interfax news agency.

"The information contained in this material bears no relation to reality."

A Facebook page called "Cargo 200," the Soviet term for the bodies of soldiers sent home from war, is also trying to protest at the use of Russian soldiers in Ukraine and connect soldiers and parents to better understand how their children died.

Yelena Vasilyeva, who helps organize the group, blamed Russia's Federal Security Services, the successor agency of the Soviet KGB, for hacking attacks.

"Our group is suffering attacks most likely from the Federal Security Services since Aug. 20. On the site it's been going on for five days," she said.

Krivenko, of the presidential human rights council, said Russia's failure to admit that its soldiers are in Ukraine is part of a long tradition of hiding military activities or playing them down, as in the first war in Chechnya.

"When the Chechen War began, it also started out without a declaration of war. And Russian soldiers participated in secret until troops were officially sent in Nov. 1994. Until then, they took off their uniforms and entered the conflict as volunteers," Krivenko said in his office at Moscow-based rights group Memorial.

"Everyone understood that there was war going on there but everyone tried to hide it in every possible way," he said.

COVERING TRACES

Rights activists and their lawyers say the biggest difference between the first Chechen War in the 1990s and now is that Russian authorities have become better at stopping information they don't like.

In the northwest Russian city of Pskov, reporters were chased away from a cemetery in late August where, according to accounts on social media, two Russian paratroopers killed in Ukraine are secretly buried.

On Aug. 21, Ukrainian journalist Roman Bochkala published on his Facebook page what he said were photographs of Russian documents recovered after Ukrainian forces clashed with an armored column of pro-Russian rebels near the village of Heorhiivka, eastern Ukraine.

The photographs show a passport in the name of a 21-year-old man called Nikolai Krygin issued in the Pskov region. There was also an insurance certificate, also issued in Pskov, and a copy of the military rule-book for Russian Airborne Troops. Reuters was unable to locate Krygin.

Pskov is the hometown of the 76th division of the Russian Airborne Troops. Its base is a few kilometers from the cemetery.

A Russian politician told Reuters he was badly beaten by unknown assailants after publicizing the funerals of the paratroopers in Pskov.

"There is a weaker civil society now. Now the entire system is closed. In a closed system, what happens covers the entire system, investigators, doctors," said Polyakova.

Vitaly Cherkasov, a human rights lawyer, said that authorities are using threats and administrative punishments - like ‘foreign agent’ status - to keep people from talking. But even with that pressure, information spreads.

Yulia Ganiyeva, 22, received a phone call from an anonymous officer on Sept. 4, informing her of the death of her fiance Alexei Zasov, 22, who served in the 31st paratroopers brigade in Ulianovsk, Vladimir Lenin's home town on the Volga river.

"They officially said that he was killed on Russian territory but the truth is that he was killed in Ukraine," she said.

"I got in touch with soldiers who served with him. They told me he was killed in Ukraine."

(Additional reporting by Denis Pinchuk in Pskov, Russia and Anton Zverev in Moscow; Edited by Simon Robinson)