The Justice Department last month requested banking records of Paul Manafort as part of a widening of probes related to President Donald Trump’s former campaign associates and whether they colluded with Russia in interfering with the 2016 election, according to people familiar with the matter.

In mid-April, federal investigators requested Mr. Manafort’s banking records from Citizens Financial Group Inc., the people said.

It isn’t clear whether Citizens is the only bank that received such a request or whether it came in the form of a subpoena. Federal law generally requires that a bank receive a subpoena to turn over customer records, lawyers not connected to the investigation said.

Citizens gave Mr. Manafort a $2.7 million loan last year to refinance debt on a Manhattan condominium and borrow additional cash, New York City real-estate records show. The Wall Street Journal couldn’t ascertain if the Justice Department request is related to that transaction or whether the bank has turned over Mr. Manafort’s records.

Separately, investigators for New York Attorney General Eric Schneiderman as well as Manhattan District Attorney Cyrus Vance Jr. also have been examining real-estate transactions by Mr. Manafort, who has spent and borrowed tens of millions of dollars in connection with property across the U.S. over the past decade, people familiar with the matter say. The request for Mr. Manafort’s banking records and the New York inquiries haven’t previously been reported.