Delta Air Lines has upped its shareholding in Hanjin KAL, parent of joint venture partner Korean Air.
Delta is now the owner of 9.21%, up from from 5.13%, according to a stock exchange filing.
"The purpose of the investment is not aimed at affecting the management rights," it said.
It has been regularly building up the stake over the past weeks with open market purchases.
Korean Air’s shares declined last month after posting disappointing second-quarter results.
It posted an operating loss of KRW98 billion.
The airline has been impacted by the trade and diplomatic dispute with Japan, which has seen several routes downsized or suspended.
However the airline sees a competitive edge with the Delta JV.
Last year, Delta added a new route linking Minneapolis/St. Paul and Seoul, and KAL launched new service between Boston and Seoul.
