DETROIT (Reuters) - General Motors Co said on Thursday that its U.S. sales rose 18 percent in August.

Don Johnson, GM's vice president for U.S. sales, said strong sales of the compact Chevrolet Cruze and SUVs Chevrolet Equinox and GMC Terrain paced the increase.

"We're carrying good momentum, and we're cautiously optimistic that we'll see U.S. economic growth improve in the months ahead," Johnson said in a GM press statement.

Flagship brand Chevrolet sales increased 16 percent. GMC sales rose the most among the No. 1 automaker's four brands, gaining 40 percent. Luxury brand Cadillac sales increased only 4 percent.

(Reporting by Kevin Krolicki and Bernie Woodall; Editing by Lisa Von Ahn)