WASHINGTON — The special counsel investigating possible ties between President Donald Trump’s campaign and Russia’s government has taken over a separate criminal probe involving former Trump campaign chairman Paul Manafort, and may expand his inquiry to investigate the roles of the attorney general and deputy attorney general in the firing of FBI Director James Comey, The Associated Press has learned.

Deputy Attorney General Rod Rosenstein told the AP in a separate interview that he would recuse himself from any oversight of special counsel Robert Mueller if he were to become a subject of Mueller’s investigation.

The Justice Department’s criminal investigation into Manafort, who was forced to resign as Trump campaign chairman in August amid questions over his business dealings years ago in Ukraine, predated the 2016 election and the counterintelligence probe that in July began investigating possible collusion between Moscow and associates of Trump.

The move to consolidate the matters, involving allegations of misuse of Ukrainian government funds, indicates that Mueller is assuming a broad mandate in his new role running the sensational investigation. The expansiveness of Mueller’s investigation was described to the AP. No one familiar with the matter has been willing to discuss the scope of his investigation on the record because it is just getting underway and because revealing details could complicate its progress.

Rosenstein acknowledged that Mueller could expand his inquiry to include Attorney General Jeff Sessions’ and Rosenstein’s own roles in the decision to fire Comey, who was investigating the Trump campaign. Rosenstein, who appointed Mueller as special counsel to take over the investigation, wrote the memorandum intended to justify Trump’s decision to fire Comey. Sessions met with Trump and Rosenstein to discuss Trump’s decision to fire him despite Sessions’ pledge not to become involved in the Russia case.

The AP asked Rosenstein specifically whether Mueller’s investigation could expand to include examining Sessions’ role.

“The order is pretty clear,” Rosenstein responded. “It gives him authority for the investigation and anything arising out of that investigation, and so Director Mueller will be responsible in the first instance for determining what he believes falls into that mandate.”

Under Justice Department rules, Mueller must seek permission from Rosenstein to investigate additional matters other than ones already specified in the paperwork formally appointing Mueller.