Photos taken by a Russian soldier have sparked controversy after it was revealed they may have been taken in Ukraine, despite Moscow's denials that its troops have intervened in the conflict across the border.

Alexander Sotkin, a 24-year-old Russian soldier and regular user of the photo-sharing app Instagram, recently uploaded a series of 'selfie' images of himself in uniform.

While the content of the photographs gives little away, the app's geolocation data showed that a number of the pictures were taken in Ukraine.

Images shared on Instagram can be "geotagged" -- which means the location of where the picture was taken is published along with the photograph.

A series of earlier images show Sotkin's location to be the village of Voloshino in southern Russia, where his unit appears to be based.

But two pictures posted on July 5 and 6 are geotagged 10 kilometres (6 miles) away, across the border in Ukraine.

First reported by the US news site BuzzFeed, the two selfies could represent proof the Russian army has crossed the border into Ukraine despite denials by the Kremlin.

While it is possible to falsify the geolocation of photos posted online, it requires a particularly advanced knowledge of coding, a computer expert told AFP.

The Russian Defence Ministry has refused to comment on the reports.

BuzzFeed said other Russian soldiers have published photographs of their activities on the Russian social network Vkontakte without geolocation data but with captions suggesting that Russia has fired artillery into Ukraine, as Kiev and Washington allege.

"We pounded Ukraine all night," wrote solder Vadim Grigoriyev on July 23 under a photo showing two artillery pieces in a wheat field with open shell boxes nearby.

Grigoriyev then appeared on a state TV channel where he denied posting them.

"They were photos taken a long time ago. Most likely my Vkontakte page was hacked," Grigoriyev said on Rossiya24.

"Grads toward Ukraine," wrote another soldier, Mikhail Chugunov, alongside two photos of a rocket launcher on Vkontakte.

UN officials have called for a halt of using the unguided missiles near populated areas.

- 'Show off to girlfriends' -

Russian MPs, meanwhile, have called for a halt to soldiers using social networking sites to share information of potential value to its foes.

"These soldiers will reveal anything -- that they are in Ukraine, for example -- just to show off to their girlfriends," Russian MP Vadim Soloviev told AFP.

Soloviev, who recently proposed a bill aimed at limiting Internet use by Russian soldiers, believes that over-sharing is a "threat to Russia," and that information "can be used by Westerners for espionage or disinformation".

"Soldiers should be subject to rules of confidentiality - and if they violate that, they should answer to the disciplinary board," the MP said.

Military expert Alexandre Golts, deputy editor of Russian website Ej.ru, told AFP it was "difficult to understand how this law could be applied," adding it would be more effective to forbid soldiers from using the Internet entirely.

"We understand why this law is needed," Golts said. "After all, it is thanks to photos posted by soldiers that the world knew that Russian special forces were present in Crimea."

Mysterious men in green fatigues, devoid of any distinctive insignia, appeared on the Ukrainian peninsula in early March, a few days before it was annexed by Russia.

Those photos prompted Soloviev, by his own admission, to push forward with the bill.

"It is exactly this scenario that Russia wants to avoid," said Golts.