A classified intelligence report obtained by The Intercept reveals that Russian hackers may have more deeply penetrated U.S. voting systems during last year's election than previously reported, including trying to hack elections officials.

The Intercept reported Monday about a "top-secret" National Security Agency document. The document — dated May 5 — details hacking efforts by Russian military intelligence that includes a cyber attack against at least one U.S. voting software supplier.

The report indicates Russian military intelligence, specifically the Russian General Staff Main Intelligence Directorate, or GRU, also sent spear-phishing emails to more than 100 local election officials days before the November presidential election.

Russian President Vladimir Putin denied last week that the Kremlin interfered in foreign elections. The House and Senate Intelligence Committee and the FBI are currently investigating Russia's actions in the 2016 presidential campaign.

CBS News also confirmed the report.