DETROIT -- Nissan Motor Co. will soon announce plans to expand production capacity in Mexico as the company aims to boost sales in North and South America, CEO Carlos Ghosn said today.

The new capacity comes as Nissan struggles to meet booming demand, especially in the United States, where sales climbed 15 percent to 1.04 million units in 2011. A key concern: the company is running out of space at its two U.S. factories to produce the hot-selling Altima sedan.

“We’re going to announce some additional capacity in Mexico in the next weeks,” Ghosn said on the sidelines of the Automotive News World Congress. “People are expecting this to happen. I’ll confirm it.”

Ghosn didn’t say what vehicle would be built with the extra capacity or say whether the expansion would come in the form of a new plant or a new line.

At full volume, Nissan’s two U.S. plants combined currently can build between 25,000 and 30,000 Altimas a month -- significantly less than the number of Camrys that Toyota can build in North America, or Accords that Honda can produce here.

Even if additional Altima production doesn’t come from Mexico, the expansion south of the border could still mean more Altima output for the United States. If Nissan can shift some other U.S.-made models to Mexico, it could free capacity for more Altimas.

In Canton, Miss., Nissan is already running three shifts on the Altima line. The Smyrna, Tenn., plant is running two shifts, but Nissan is currently adding three new models to the Smyrna plant: the Nissan Rogue crossover and electric Leaf sedan, and the Infiniti JX crossover.

Japan’s Nikkei business newspaper reported last month that Nissan plans to double its capacity in Mexico to 600,000 units a year by building a new factory.