TOKYO—Bridgestone Corp. reported an increase of 18.1 percent in operating income in the first quarter to $806.9 million.

Sales rose 9.4 percent to $8.62 billion, and net income rose 2.1 percent to $467.6 million.

In the tire segment, sales grew by 12.1 percent to $7.32 billion, while the company’s operating income jumped 19.1 percent to $736.4 million, or 10.1 percent of revenue.

Bridgestone did not elaborate on the reasons for its earnings improvements, but it said the sales gains reflected the recovering economies in Japan and the U.S.

In Japan unit sales of tires for passenger cars and light trucks decreased compared to the first quarter of 2012, due to a decline in the sales of original equipment tires, Bridgestone said.

In North America, unit sales of tires for passenger cars, light trucks, trucks and buses increased steadily. The company also saw an increase in China for all types of tires, though it noted that there was a slowdown in the Asian economy, particularly in China and India.

In Europe, sales of tires for passenger cars and light trucks decreased due to a decline in sales of original equipment tires. By contrast, unit sales of tires for trucks and buses increased strongly due to an increase in replacement tires. Bridgestone said the European economy remained stagnant and “continuous financial instability” discouraged actual business activities.

Sales revenue in the Americas grew 17.4 percent to $3.98 billion, Bridgestone reported. Operating income for the region jumped 35 percent to $389.3 million.