KIEV — Since the beginning of the conflict in eastern Ukraine, Ukrainian authorities have repeatedly reported arrests they say they've made of numerous Russian citizens fighting on the side of the pro-Russian militia. Moscow has always promptly denied such reports.

But new details have come to light that lend weight to Kiev's claims after Ukraine's special services said they had arrested a Russian FSB agent on June 30. The FSB (Federal Security Service) is the main successor of the Soviet KGB.

The Ukrainian forces say Igor Kimakovsky, a 43-year-old former university teacher from St. Petersburg, admitted he had been enlisted by Russian special forces back in 2008 and had been collecting information about "Ukrainian armed forces, Russian citizens fighting on the Ukrainian side as well as the social and economic state of the occupied territories."

This was backed up by the mayor of the city of Debaltseve in the Donetsk region, Alexander Afendikov, who told Kommersant that Kimakovsky had been regularly visiting the region since October 2014. He had acted as his advisor and appeared to have come to the Donbass region to help rebuild destroyed homes and distribute humanitarian aid.

An educated man

"He came sometime in March, when Debaltseve had already been taken," Afendikov said. "Until then, he was a university professor, an educated man we were glad to have here. He was a volunteer: helping rebuild destroyed houses and he came up with different programs to help the locals."

Afendikov also noted that before his trip to St. Petersburg, Kimakovsky had appealed to Ukrainian security representatives to control the humanitarian situation in the city and keep an eye on what aid was going to Debaltseve and how it was distributed.

Igor Kimakovsky used to be the director at St Petersburg's Centre of Information Technology, and allegedly would inform the FSB about student demonstrations in St Petersburg. Former students told Kommersant that Kimakovsky would arrange for the distribution of military-patriotic crosses and would travel regularly to the Chechen capital of Grozny.

Neither the university he worked at nor the Russian Defense Ministry would comment on Kiev's claims.

Also, in May, pro-Ukrainian forces arrested two men it said were Russian soldiers in Lugansk. The Russian Defense Ministry continues to insist that there is no Russian military presence in the region, and that those arrested were ex-soldiers, and demanded their release.

Also in May, Ukrainian President Petro Poroshenko said that in the course of a few months, some 80 soldiers from Russian special units had been captured.

The Russian government has refused to comment on the latest detention, but said they would "make every effort at rescuing illegally detained Russian citizens abroad."

The Ukrainian security forces have not commented on Kimakovsky's fate, but the mayor of Debaltseve is hoping he can negotiate for his release through a prisoner exchange.