Thirteen Russian nationals and three entities have been indicted for allegedly breaking U.S. laws to interfere with the 2016 presidential election, Deputy Attorney General Rod Rosenstein announced Friday. CBS justice reporter Paula Reid says there probably won't be any arrests soon -- because it's "highly unlikely" Russia will extradite any of those indicted. The indictment is significant because it lays out specific details about how Russia meddled in the 2016 election and what crimes were committed under U.S. law.

Although the indictment doesn't mention the Russian government, CBS News senior national security analyst Fran Townsend said that judging by the size and scope, it's "impossible to think" the operation could have been carried out without the blessing of the Kremlin.

CBS News chief national security analyst Fran Townsend and CBS News justice reporter Paula Reid. CBS News

On Friday, a D.C. federal grand jury returned an indictment against the Internet Research Agency, a Russian organization which has connections to Russian President Vladimir Putin. It names 13 Russian nationals and three Russian entities and accuses them of violating U.S. criminal laws to meddle in U.S. elections and political processes. According to a spokesman for the special counsel's office, the indictment charges all of the defendants with conspiracy to defraud the U.S., as well as "three defendants with conspiracy to commit wire fraud and bank fraud, and five defendants with aggravated identity theft."

Reid noted that the indictment shows that special counsel Robert Mueller's investigation continues to move forward. Mueller is still looking into any possible financial transactions between the Trump campaign and Russia -- and speaking to witnesses about the question of obstruction of justice.

"Earlier this week, [Mueller] spoke with former chief strategist Steve Bannon and just yesterday, interviewed former legal team spokesman Mark Corallo," Reid said. "So despite these claims from the White House that this is all wrapping up soon, what we know is that this investigations and the trials they need to put on, this is going to last well into this year and probably into next."

There's no allegation that any American was knowingly involved in the conspiracy, Rosenstein said Friday. But one thing Townsend zeroed in on in the indictment is the mention of an "unidentified American" who assisted.

"Everybody ought to assume that unidentified American is cooperating with Bob Mueller, probably has taken a guilty plea that may or may not be sealed. And the question is what does that unidentified American know about any connection to either political campaign here in the United States -- specifically the Trump campaign," Townsend said.

That person was helping them target people in swing states, according to the indictment. "That person is key to understanding what other Americans may be involved in this."