A soldiers' rights group cast doubt on Monday on denials by military prosecutors in Moscow that a Russian serviceman was on active duty when captured fighting in Ukraine.
The Kremlin and Russia's military say Alexander Alexandrov, captured with a colleague on May 16, had quit Russia's military before going to east Ukraine to fight alongside pro-Russian separatists.
Alexandrov denies he had resigned his commission and the Union of Soldiers' Mothers' Committees, to whom he has turned for help, says Russian military prosecutors provided no proof he had quit when it requested more information on the case.
"It's not that easy to quit the army if you have a contract," Valentina Melnikova, who heads the group, told Reuters by telephone and quoted the response about Alexandrov.
"The events related to his departure from the Russian Federation and his stay on the territory of Ukraine took place after his resignation and were not related to his military service."
Alexandrov, whose leg was shattered in the fighting, is being treated in a Kiev military hospital along with Captain Yevgeny Yerofeyev, another Russian captured during the same battle.
Russia denies accusations by Western governments and Kiev that it has sent troops and weapons to separatists in eastern Ukraine in a conflict in which about 6,400 people have been killed since April 2014.
Echoing statements by the Kremlin, Russia's military has said Alexandrov resigned from his special services unit before going to Ukraine. His wife also said this but Alexandrov has said she did so under pressure and his mother told Reuters last week he had said nothing to her about resigning.
The Russian Chief Military Prosecutor's Office, contacted by telephone, said it was unable to comment immediately to Reuters.
Melnikova, who has defended soldiers' rights since Russia's 1994-96 war against Chechen separatists, said the response received from the military prosecutors looked weak.
"The response is insulting for us. The Chief Military Prosecutor's Office has never sent us such empty responses before," she added.
Melnikova said she would now apply to the chief military prosecutor personally to complain that the authorities had given no details to show they had looked into the case properly.