WASHINGTON, D.C. - CBS News has confirmed with multiple sources that a federal grand jury has approved charges in connection with the investigation into Russian meddling in the U.S. presidential election, and the sealed indictment is expected to be made public sometime Monday. An arrest is expected as early as today in connection with special counsel Robert Mueller's probe.

When that happens it will signal a new phase in the Russia investigation, as Mueller moves to prosecute more suspects, reports CBS News correspondent Jeff Pegues.

On Sunday, lawmakers highlighted the seriousness of a federal grand jury approving charges in connection with the Russia investigation.

"It's really important what the charge is. It's really important who the person being charged is," South Carolina Rep. Trey Gowdy said on Fox News. 

"There are two people I think just from press reporting that is likely to be: either Mike Flynn or Paul Manafort," California Rep. Adam Schiff said on ABC News.

Manafort was the Trump campaign chairman between May and August of 2016. But prior to the campaign, he was a prominent Washington lobbyist. His dealings in Ukraine have come under scrutiny because of his ties to Russian oligarchs connected to the Kremlin and Russian President Vladimir Putin.

Manafort, along with Carter Page, who was a foreign policy adviser for the Trump campaign; the president's son, Donald Trump Jr.; the president's son-in-law, Jared Kushner; and former National Security Adviser Michael Flynn have all been under scrutiny. 

Flynn was fired in February after misleading the vice president about his contacts with Russian officials.

Former U.S. attorney Preet Bharara says the first arrest is likely to be someone who has information that can advance the overall investigation.

"Prosecutors like those in my former office and those that work in Bob Mueller's office now try to see who they can bring charges against first and see if they have information about someone else," Bharara said on CNN.

Manafort's attorneys said they have not heard that their client had been indicted, while Flynn's attorneys did not respond to our requests for comment. As far as who leaked the indictment, Rep. Gowdy said it should not be overlooked that someone violated the law by disclosing grand jury material.

© 2017 CBS Interactive Inc. All Rights Reserved.