LONDON — Russian hackers over the past 12 months have tried to attack the British energy, telecommunications and media industries, the government’s top cybersecurity official said Tuesday in a summary of a speech to be delivered on Wednesday.

The warning, by Ciaran Martin, chief of the National Cyber Security Center, is the strongest indication yet that Russian cyberattacks on Western governments and industries may be far more persistent than United States or British officials have previously acknowledged.

The speech also appeared to fit into a coordinated effort by the British government to publicly warn Russia that its efforts have been noticed. In a speech on Monday night, Prime Minister Theresa May addressed Russia directly. “We know what you are doing,” Mrs. May said. “And you will not succeed.” She accused the Kremlin of “threatening the international order on which we all depend.”

Taken together, the two speeches are a sharp escalation in the public accusations around a conflict that has so far remained mostly in the shadows. Recent high-profile cyberattacks, however, have put new pressure on politicians to defend against the dangers.