By Jonathan Landay WASHINGTON (Reuters) -The United States believes that Iran is involved in the planning and execution of drone and missile attacks by Yemen’s Houthi group on Israel and ships in the Red Sea, a senior aide to U.S. President Joe Biden said on Thursday. The comments by deputy White House national security adviser Jon Finer are among the most explicit to date by a U.S. official alleging Iranian involvement in the Houthi attacks. Finer spoke hours after the United States imposed new sanctions aimed at throttling what U.S. officials say is Iranian financial support for the Houthi s…