“We made a serious offer ... and we urge the Russians to accept it, because we made it with all sincerity,” RIA Novosti quotes him.
Kirby kept silent about the details of a possible deal.
Earlier, CNN, citing sources, reported that US President Joe Biden supported a plan to exchange Bout for Brittney Griner and Paul Whelan.
Also, according to the channel, Russia allegedly asked the United States for an exchange list, in addition to Viktor Bout, Russian Vadim Krasikov.
Later, White House spokeswoman Karine Jean-Pierre said that the United States received a counter offer from the Russian side regarding the exchange of prisoners, but considered it "frivolous."