The U.S. Commerce Department said on Thursday it was launching an investigation that could lead to steep import duties on more than $100 million worth of wind energy towers from China and Vietnam.

The decision adds to the friction in clean energy trade between the world's two largest economies.

The department said it was also launching a separate probe into allegations of unfairly priced steel wire garment hangers from Vietnam and Taiwan.

The Commerce Department is already investigating charges that Chinese solar panel manufacturers engage in unfair trade practices and will issue a preliminary decision on duties next month.

The Wind Tower Trade Coalition, a group of U.S. producers, is asking for anti-dumping duties of 64 percent on imports from China and 59 percent from Vietnam. They also want additional countervailing duties on imports from China to offset alleged government subsidies.

A separate U.S. government agency, the International Trade Commission, held a hearing on Thursday to probe whether U.S companies have been materially harmed or threatened by the imports. The ITC has the final word on whether any U.S. duties are imposed.

Kerry Cole, president of Trinity Structural Towers, told the panel that domestic producers suffered a severe blow when none of their towers was selected for the 338-tower Shepherds Flat project in eastern Oregon, which is due to be completed next year and is billed as the world's largest wind farm.

"All of it went to China ... This lone lost sale had ripple effects throughout the industry ... After losing this sale, domestic producers were desperate to fill their order books," putting them under tremendous pressure to cut prices, Cole said. (Reporting By Doug Palmer; Editing by Doina Chiacu and Vicki Allen)