WASHINGTON U.S. businesses maintained a fairly solid pace of inventory investment in September amid rising sales, government data showed on Wednesday.

Business inventories rose 0.4% after rising by the same margin in August, the Commerce Department's Census Bureau said. The increase in inventories, a key component of gross domestic product, was in line with economists' expectations.

Inventories rose 1.3% on a year-on-year basis in September.

Private inventory investment added 1.32 percentage points to the economy's 4.9% annualized growth pace in the third quarter. Business boosted inventory accumulation to meet strong demand.

Retail inventories increased 0.9% in September as estimated in an advance report published last month. They rose 1.0% in August. Motor vehicle inventories advanced 2.1%, rather than 2.2% as estimated last month. They increased 2.4% in August.

Retail inventories excluding autos, which go into the calculation of GDP, rose 0.4% instead of 0.3% as previously reported. They gained 0.5% in August.

Wholesale inventories rose 0.2%, while stocks at manufacturers increased 0.2%.

Business sales climbed 1.1% in September after rising 1.4% in August. At September's sales pace, it would take 1.36 months for businesses to clear shelves, down from 1.37 months in August.

(Reporting by Lucia Mutikani; Editing by Chizu Nomiyama)