KKR & Co. (KKR), the private-equity firm run by Henry Kravis and George Roberts, will more than double its stake in a unit of Vietnam’s Masan Group Corp. (MSN) to $359 million, its biggest investment in Southeast Asia.

The U.S. firm will invest an additional $200 million in Masan Consumer Corp., a Vietnamese fish sauce maker, the largest private-equity deal in the country, according to a joint statement Wednesday. KKR bought a 10 percent stake for $159 million in April 2011, its first acquisition in Vietnam.