Several dozen women gathered outside a military base in central Russia on Thursday to demand that commanders come clean about the whereabouts of their husbands after reports of secret funerals for soldiers covertly sent to Ukraine.

The women -- mostly in their 20s, a few with small children -- huddled outside a base that houses paratroopers in Kostroma, around 300 kilometres (200 miles) north of Moscow.

Some 350 soldiers from the city were this month sent on military drills to the border with Ukraine and then went incommunicado, said one of the women, 26-year-old Valeria Sokolova.

Commanders from the base have told her several have returned dead, she said, and around 15 wounded soldiers were also flown back this week.

"Cargo-200 arrived yesterday," Sokolova said, citing military officials and using the Russian army term for body bags.

Funerals for those killed are expected to be held in the town on Friday.

The women stood outside the drab base with banners extolling the "beloved troops of the motherland", but military commanders refused to confirm that their loved ones had been sent to Ukraine, Sokolova said. They were told they could not hold a formal demonstration and should go home.

"They would only tell us that they are not in Russia," she said.

Her last communication with her husband was on Saturday when he told her that he and his comrades were being deployed, without saying the destination.

"Some will ride in tanks and I will be in a Kamaz (truck)," her 25-year-old husband told her, adding that he had been told to take winter clothes.

A man who interacted with the women outside the base wore civilian clothes and gave his name as Albert Akhmerov but did not state his role.

He said the soldiers were taking part in military drills.

"Your children will be proud of their fathers," he told the women. "They are honest Russian warriors."

- Phone call from Kiev -

Olga Garina, the mother of one of several Kostroma paratroopers captured by Ukrainian forces, is one of the lucky few to have gotten some answers.

After days of silence and heartache after he went off the radar, her 20-year-old son Yegor Pochtoyev called her mobile phone suddenly from Kiev, where he is being held by authorities.

She happened to receive the call while sat with a group of journalists including AFP in the office of a local rights group that campaigns against abuses in the armed forces.

"My baby, I love you. I am fighting for you," she cried out.

After the emotional phone call, Garina covered her face with her hands and burst into tears.

Garina, Sokolova and several other women said that despite everything they supported Putin's policies.

- 'Only fresh graves' -

NATO said on Thursday that "well over a thousand" Russian troops are operating inside Ukraine.

Russian independent media this week reported on secret funerals held for several soldiers in northwestern Russia, citing mourners who said they were killed in Ukraine.

Officials said they are looking into the reports but refused to confirm that troops had been sent to Ukraine.

President Vladimir Putin said this week that Russian soldiers captured in Ukraine had crossed the border by accident while on routine patrol.

Critics have drawn parallels with the official denials earlier this year from the Kremlin that paramilitary forces had been sent to Crimea prior to its annexation by Russia. The government later admitted the soldiers had operated in the peninsula and awarded some with medals for their service.

Parallels have also been drawn to the early days of the Soviet war in Afghanistan, which was officially denied when it began in 1979. Bodies returning from Afganistan were buried in secret.

Moscow's opposition media launched an awareness campaign about Russian soldiers in Ukraine this week.

There is no official war with Ukraine, wrote the editor of Dozhd TV, Mikhail Zygar, on his blog. "There are only fresh graves and the bodies of the soldiers who no one recognises as dead."