The only reason why they're denying it is because they didn't do it, or at least it wasn't ordered by Zelensky.

Local and regional authorities in Russia have reported a series of drone strikes in recent months. Some have landed close to Ukraine’s border with Russia, but at least one has hit south of Moscow. Ukraine has not acknowledged responsibility for most of the incidents. Moscow is around 280 miles northeast of the Ukrainian border at its closest point.

Last month, The Washington Post reported that the United States had secretly monitored discussions among Ukrainian officials about possible attacks against Moscow timed to coincide with the Feb. 24 anniversary of Russia’s invasion. The White House feared that such a move would provoke an aggressive response from Moscow, and two days before the anniversary, the C.I.A. said that Ukraine’s intelligence directorate “had agreed, at Washington’s request, to postpone strikes” on Moscow. The information was part of a trove of classified U.S. intelligence documents obtained by The Post and other news organizations.