Ketchum has a global contract with the Russian Federation, which also works with UK public affairs agency Portland Communications and Brussels-based public affairs agency GPlus Europe.
All three agencies are part of the US-headquartered marketing services group Omnicom.
Ketchum clarified its work amid the tension between Europe and Russia over each side's alleged interventions in Ukraine.
An agency spokesperson said: "Ketchum's work with the Russian Federation began in 2006 when Ketchum was hired to provide public relations counsel and media relations support to the presidential press office as the country prepared to host the G8 Summit in St Petersburg.
"Our work continues to focus on supporting economic development and investment in the country and facilitating the relationship between representatives of the Russian Federation and the Western media.
"We are not advising the Russian Federation on foreign policy, including the current situation in Ukraine."
Portland's work is understood to include public affairs monitoring, though the agency declined to comment.
GPlus Europe also declined to comment.
On Wednesday, Pleon Talan, Ketchum's PR agency unit in Ukraine, posted a message on Facebook from its general PR director Irina Zolotarevych about media reports it called "unbalanced and a threat to the reputation of Pleon Talan". The stories implied that Ketchum is "responsible for the anti-Ukrainian propaganda in the foreign media", according to the post.
The post also said that the articles did not verify facts or include an official response from the Omnicom Group agency, and it could cause readers to think Pleon Talan is involved in government issues.
Zolotarevych added in the Facebook post that Pleon Talan is "never involved in any anti-Ukrainian actions or projects either in Ukraine or abroad," and it "did not initiate nor embody any project that supports Russian aggression against Ukraine or vice versa".
The post also said Pleon Talan "does not work and has never been involved in work with the Russian government".