A Moscow court late on Wednesday ruled to designate Navalny's regional offices and his Anti-Corruption Foundation (FBK) as "extremist", barring them from working in Russia.
The US State Department called the action "particularly disturbing" and said it was part of a pattern of restricting fundamental rights in Russia.
In a radio interview on Thursday morning, Russian Foreign Ministry spokeswoman Maria Zakharova said the response showed the extent of US interference in Russia's affairs.
"Can you imagine seeing such an instant reaction from the State Department to a domestic or some other internal decision in another country?" she said in the interview broadcast on YouTube and state radio.
"Then in a few hours they make a special statement. This means that they are politically involved in the story," she said, adding that Washington was thus exposing its "agents".
"They show such political zeal because it touches those whom they supervised, those whom they supported politically and in other ways," Zakharova said.
Prosecutors in April had requested that Navalny's organisations be hit with the "extremist" label, saying the group was plotting an uprising with support from the West.
Navalny's network of regional offices had helped organise a smart voting strategy that urged voters to cast ballots for those most likely to defeat Kremlin-linked candidates.
Ahead of parliamentary elections in September -- in which the deeply unpopular ruling United Russia party is expected to struggle -- lawmakers passed legislation that bans members and sponsors of "extremist" groups from running in the polls.
