SEOUL, South Korea — North Korea could deploy a new rocket system as early as this year that would expand its ability to strike South Korean and American military forces in the South, South Korea’s defense minister said on Wednesday.

South Korea has been closely monitoring the North’s development of the 300-millimeter multiple-rocket launcher system, which the country has tested frequently in recent years. The weapon has alarmed officials because it is believed to have a range long enough to strike major American and South Korean military bases, including those near Pyeongtaek, about 60 miles south of Seoul, the capital.

Defense Minister Han Min-koo said on Wednesday that North Korea was likely to deploy the new system late this year at the earliest. The North developed the weapon because it is cheaper than its short-range, Scud-type ballistic missiles and allows it to fire far more projectiles, Mr. Han said in an interview with South Korean reporters.