Email accounts of officials at a Republican group that supports party candidates running for the U.S. House of Representatives were hacked in early 2018, ahead of this year's Congressional elections, according to a person familiar with the situation.

Hackers used stolen passwords to access a "small number" of National Republican Congressional Committee (NRCC) email accounts in a relatively unsophisticated hack discovered around April, said the person, who was not authorized to discuss details of the attack.

The NRCC quickly fixed the problem by changing the passwords on accounts at its web-based email provider and taking steps to protect the organization from similar attacks, the person said.

The person declined to name the email provider.

NRCC spokesman Ian Prior confirmed via email that the group was the victim of a cyber attack by an unknown party, but declined to say what systems were affected.

"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," Prior said.

He declined to elaborate. The news was first reported by Politico.