US Attorney Preet Bharara’s probe into Gov. Cuomo’s controversial “Buffalo Billion” revitalization plan now involves his inner circle — including one of his longtime former aides, sources said Friday.

Federal investigators have slapped the governor’s office with subpoenas for documents related to improper lobbying and conflicts of interest, according to sources.

Sources say the probe has “zeroed in” on several people with close ties to Cuomo, among them Joseph Percoco, one of the governor’s longest-serving aides, who is now a chief executive at the Madison Square Garden Co.

“This investigation has recently raised questions of improper lobbying and undisclosed conflicts of interest by some individuals which may have deceived state employees involved in the respective programs and may have defrauded the state,” Cuomo counsel Alphonso David said in a statement.

“The governor has ordered an immediate full review of the program,” David wrote.

Cuomo also announced that lawyer Bart Schwartz, who previously served as chief of the Criminal Division in the Manhattan US attorney’s office, will be monitoring the “Buffalo Billion” program.

Asked about Percoco, Cuomo’s office declined comment. Percoco had no immediate comment.

“There’s no one closer to Cuomo than Percoco, and if he sings, well, the feds go after the big fish,” one Albany insider said.

The probe also includes Buffalo developer and big-time Cuomo donor Louis Ciminelli, lobbyist Todd Howe, SUNY high-tech official Alain Kaloyeros and an energy company called Competitive Power Ventures, sources said.

State employees are now barred from dealing with Howe, who is president of the lobbying firm WOH Government Solutions and once served as Cuomo’s deputy chief of staff at the Department of Housing and Urban Development, a Cuomo administration source said.

They also may not communicate with Competitive Power Ventures.

Additional reporting by Danika Fears