TOKYO—Panasonic Corp. executives sought to allay investor concerns about the firm taking part in Tesla Motors Inc.'s $5 billion plant, saying any investment decision will be made one step at a time, in line with market demand.

Earlier this month, the Japanese tech giant said it signed a letter of intent to participate in the construction of what the Silicon Valley electric-car maker calls "gigafactory" for assembling vehicle batteries in the U.S. But Panasonic hasn't disclosed how much it plans to invest in the plant.

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