(Reuters) -Citigroup's ( C/PN ) chief accounting officer and controller Johnbull Okpara resigned to pursue another opportunity, effective Tuesday, the bank said in a filing.

Robert Walsh, who has served as controller for Citi's services business since November, will take on the role of interim chief accounting officer while the bank searches for a permanent replacement for Okpara.

Patrick Scally will act as its interim controller.

"Johnbull will stay at Citi to drive the third quarter earnings process and then will advise as needed through the filing of the 10Q to ensure a seamless transition," Chief Financial Officer Mark Mason wrote in an internal memo, referring to a quarterly regulatory filing.

In Okpara's nearly four years at Citi, he "has overseen critical efforts to strengthen our financial and regulatory reporting, internal controls and accounting policies," Mason wrote in the memo seen by Reuters.

The bank declined to comment beyond the filing and memo.