Congressional leaders were first notified a year ago that Russian hackers had infiltrated computer systems affiliated with the Democratic Party, Reuters reported Friday.

The handful of lawmakers who received a Top Secret intelligence briefing regarding the cyber attacks were barred from disclosing the breaches to Democratic National Committee officials.

U.S. intelligence officials briefed a group of eight congressional leaders last summer that two Russian intelligence agencies were targeting the DNC’s computer network. American spy agencies continued to monitor the hackings to collection information regarding their tactics.

Lawmakers are now considering sanctions against Russia in response to the breaches, but the action would require the White House to formally accuse Moscow of the cyber attacks, the Wall Street Journal reported. The U.S. typically does not publicly disclose the perpetrators of cyber attacks.

DNC officials said they were not informed of the breach until last fall after an FBI cyber security agent asked about the party’s data security arrangements, according to Reuters. Still, the FBI did not inform them that U.S. intelligence officials suspected Russian government hackers were behind the attacks.

House Minority Leader Nancy Pelosi called the incident an "electronic Watergate" on Thursday and said she knew "for sure" the breaches were the work of the Russians. She was among the lawmakers briefed on the attacks last summer.

Other Democratic lawmakers who attended the intelligence briefing included Senate Minority Leader Harry Reid and intelligence committee leaders Sen. Dianne Feinstein and Rep. Adam Schiff. The Republicans included Senate Majority Leader Mitch McConnell, former House Speaker John Boehner, and intelligence committee heads Sen. Richard Burr and Rep. Devin Nunes.

The group was informally known as the "Gang of Eight."

The FBI publicly announced last month that its agents were investigating the DNC hack after troves of stolen documents were released by WikiLeaks. The leak forced the resignation of former DNC chair Debbie Wasserman Schultz because of emails suggesting the party favored Hillary Clinton over Sen. Bernie Sanders (I., Vt.) during the Democratic primary.

Russia has denied involvement in the attacks.

Interim DNC Chair Donna Brazile said Thursday she intended to create a Cybersecurity Advisory Board aimed to prevent "future attacks and ensure that the DNC’s cyber security capabilities are best-in-class," according to a memo obtained by Reuters.

Reports surfaced Wednesday finding that the breaches were broader than initially thought after officials confirmed the personal email accounts of more than 100 party officials were breached. Many of those hacked were Clinton campaign staff and party operatives.

Investigators confirmed nearly two weeks ago that Russians breached the Democratic Congressional Campaign Committee, the campaign arm for House Democrats, in an incident that paralleled the earlier cyber attack on the Democratic National Committee.

Democrats involved in the FBI probe said the agency now believes the hack may have extended to the Democratic Governors Association.