House Speaker Paul Ryan, R-Wis., said Friday that the Russians took part in a "sinister and systematic attack" on the U.S. political system, after Deputy Attorney General Rod Rosenstein announced indictments of 13 Russian nationals and three Russian entities for meddling in the 2016 election.

“We have known that Russians meddled in the election, but these indictments detail the extent of the subterfuge," Ryan said of the indictments stemming from special counsel Robert Mueller's investigation.

"These Russians engaged in a sinister and systematic attack on our political system," Ryan said. "It was a conspiracy to subvert the process, and take aim at democracy itself.

"Today’s announcement underscores why we need to follow the facts and work to protect the integrity of future elections," Ryan added.

According to Mueller's office, all 13 were indicted on charges of conspiracy to defraud the United States, while three defendants were charged with conspiracy to commit wire fraud and bank fraud. Five defendants were also charged with aggravated identity theft.

Rosenstein said at a press conference Friday afternoon that the push to interfere with the 2016 election started in 2014 and ultimately looked to harm the campaigns of former Secretary of State Hillary Clinton, Sen. Marco Rubio, R-Fla., and Sen. Ted Cruz, R-Texas, by purchasing ads on social media platforms in the names of American citizens and entities.