Apollo Global Management Inc. has agreed to acquire Sector Financial Inc., which focuses on middle-market lending, as part of its purchase of part of Credit Suisse Group AG’s securitized products group, according to people with knowledge of the matter.

Details, including valuation as part of the larger transaction, couldn’t immediately be learned. Apollo and Credit Suisse spokespeople declined to comment. Representatives for Sector didn’t immediately respond to requests for comment.

Chevy Chase, Md.-based Sector is an affiliate of Credit Suisse. It provides loans to finance growth, acquisitions, working capital and other efforts, its website shows. Led by CEO Todd Gordon and president Thomas Pagnani, Sector also has offices in New York and Chicago.

Private credit has ballooned to a $1.3 trillion global market. Financial institutions, including alternative asset managers, have launched private-credit units in a move that has enabled them to gain market share from banks.

Sector focuses on borrowers in industries including health care and technology, providing loans from $10 million to more than $100 million. It also offers asset-based loans, commercial mortgages, auto receivables and leveraged loans, and counts LendingUSA among prior borrowers.

New York-based Apollo operates a mid-market debt-origination platform known as MidCap Financial. Zurich-based Credit Suisse has said it’s transferring a large portion of SPG assets to Apollo, which is taking on most of the unit’s employees.