The first charges have been filed in Mueller's Trump-Russia investigation

The first criminal charges to result from FBI special counsel Robert Mueller's investigation into Russia have been filed.

What happened?

A federal grand jury on Friday approved the first charges in the investigation, according to CNN. However, it is unclear what the charges are because a federal judge ordered they remain sealed.

Sources told CNN that the first arrests are imminent and could happen as soon as Monday. More from CNN:

On Friday, top lawyers who are helping to lead the Mueller probe, including veteran prosecutor Andrew Weissmann, were seen entering the court room at the DC federal court where the grand jury meets to hear testimony in the Russia investigation.

Reporters present saw a flurry of activity at the grand jury room, but officials made no announcements.

What is Mueller's investigation looking for?

Mueller was appointed by Deputy Attorney General Rod Rosenstein in May to take control of the FBI's investigation into President Donald Trump's campaign and Russia. Attorney General Jeff Sessions recused himself. The focus of Mueller's investigation has mostly centered in three areas:

• Any potential ties, including collusion, between Trump's campaign and Russia
• Any effort by Trump to obstruct justice by impeding the investigation, especially after he dismissed James Comey as FBI director in May
• And any financial connections Trump or his campaign, or any of his associates, may have had to Russia

The investigation has been the center of intense scrutiny, mostly because Trump's supporters believe it is focused mostly on Trump, despite the president allegedly being innocent of any wrongdoing. Nevertheless, the investigation has trudged forward. Trump has labeled it a "witch hunt."

Reuters has also confirmed the story.