WASHINGTON — The campaign arm of the House GOP was hacked during the 2018 campaign cycle, it was reported Tuesday.

The email accounts of four top National Republican Congressional Committee officials were surveilled for several months and the break-in was discovered in April.

But the three top House Republicans — Speaker Paul Ryan of Wisconsin, Majority Leader Kevin McCarthy of California and Majority Whip Steve Scalise of Louisiana — weren’t informed of it, Politico reported.

Rep. Steve Stivers (R-Ohio), the House member in charge of the committee during the 2018 cycle, did not respond to Politico’s repeated requests for comment.

The hack was detected by MSSP, a vendor the NRCC uses to monitor its network.

At the time, an investigation was launched. None of the emails accessed have been released to the public, nor were NRCC officials threatened by the perpetrators with such an action.

Committee officials said they kept quiet about the hack so as not to compromise the investigation.

While there’s no official word on who was responsible, officials privately told the news site they believed it was a foreign agent.

“The NRCC can confirm that it was a victim of a cyber intrusion by an unknown entity. The cybersecurity of the Committee’s data is paramount, and upon learning of the intrusion, the NRCC immediately launched an internal investigation and notified the FBI, which is now investigating the matter,” said Ian Prior, a former Justice Department official now employed by Mercury Public Affairs, the outside firm the NRCC hired to handle the hack.

The news comes on the heels of Defense Secretary James Mattis confirming that Russia tried to meddle in the election, though he didn’t offer any specifics.

“[President Vladimir Putin] tried again to muck around in our elections this last month, and we are seeing a continued effort along those lines,” Mattis told a crowd Saturday at a conference in California.