MOSCOW — Russia has ordered the United States to end its financial support for a wide range of pro-democracy, public health and other civil society programs here, in an aggressive step by the Kremlin to halt what it views as American meddling in its internal affairs.

The Kremlin’s provocative decision to end two decades of work in post-Soviet Russia by the United States Agency for International Development — with little warning ahead of an Oct. 1 deadline — was announced on Tuesday by the State Department in Washington. The move stands to cut off aid that currently totals about $50 million a year, a relatively small sum but a potentially devastating blow for groups that came to rely on foreign money as domestic controls over politics tightened.

American officials, who were informed of the decision earlier this month, quickly pledged to maneuver around the Kremlin. The Obama administration last October proposed the creation of a new $50 million fund— essentially an endowment for a private foundation established under Russian law — for Russian civil society groups, and one senior administration official said work on that project would speed up.

The Kremlin has taken a number of actions in recent months to bring pressure on nongovernmental groups and clamp down on political dissent, including a new law requiring any organization receiving aid from abroad to register with the justice manager as “acting as a foreign agent.” Russia also increased the penalties for libel and slander — a step that seemed intended to intimidate critics of government officials.