Mitsubishi Motors Corp. is set to end U.S. vehicle production and will likely enter negotiations to sell its only plant in the country to another car maker, a person with knowledge of the matter said Friday.

The move, first reported by the Nikkei business newspaper, underscores the second-tier Japanese car maker's strategy to focus on Southeast Asia, its biggest market, as it faces struggling sales in the U.S.

Mitsubishi sold 82,000 vehicles in the U.S. in the fiscal year that ended in March, holding around a 0.5% market share, the company said. The U.S. accounted for around 8% of Mitsubishi's global sales of 1.1 million vehicles, it said.

The auto maker's Normal, Ill., plant began production in 1988 as a joint venture with former partner Chrysler. Last year, Mitsubishi made 64,000 Outlander Sport sport-utility vehicles at the plant, substantially under its annual capacity of 122,000 vehicles, according to the company.

The facility is the only unionized U.S. plant among Japanese car makers, with its workers represented by the United Auto Workers union. Around 1,250 people work at the plant, according to Mitsubishi.

In 2012, Mitsubishi ended car production in Western Europe, selling its Netherlands plant to bus maker VDL Groep for €1 ($1.10) on the condition that the facility's workers would keep their jobs.

The auto maker is set to announce its first-quarter earnings on July 30.

Write to Yoko Kubota at yoko.kubota@wsj.com

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