“I cannot rule it out,” he said in an interview. “He has a good background. He is one of my old friends. I have good friends in South Ossetia and in Grozny.”

Some observers have asked whether the man photographed in Georgia is the same person photographed in eastern Ukraine.

Another question has been raised about a group photograph of uniformed men who are identified in the Ukrainian submission as a “sabotage-reconnaissance group” that reports to the “General Staff of the Russian armed forces.”

The Ukrainian submission to the Organization for Security and Cooperation in Europe does not identify where the group photograph was taken but asserts that one prominently featured soldier was involved in operations in eastern Ukraine.

A packet of American briefing materials that was prepared for the Geneva meeting asserts that the photograph was taken in Russia. The same men are also shown in photographs taken in Ukraine. Their appearance in both photographs was presented as evidence of Russian involvement in eastern Ukraine. The packet was later provided by American officials to The New York Times, which included that description of the group photograph in an article and caption that was published on Monday.

The Western allegations that Russia has intervened in Ukraine are based on NATO’s analysis of the tactics employed by armed groups in eastern Ukraine; Ukraine’s assertion that it has arrested several Russian intelligence officers; the accounts of local residents and news media reports; and classified information. But the dispute over the group photograph cast a cloud over one particularly vivid and highly publicized piece of evidence.

Maxim Dondyuk, a freelance photographer who was working in Slovyansk principally for the Russian newsmagazine Russian Reporter, said that he had taken the group photograph there and posted it on his Instagram account.