The United States is opening a "Section 301" investigation into whether Vietnam has been undervaluing its currency and harming U.S. commerce, the U.S. Trade Representative's office said in a statement on Friday.

It also announced investigation into Vietnam's harvesting and trading of timber in the same statement.

The so-called "Section 301" investigation, under an U.S. trade law adopted in 1974, allows the U.S. president to unilaterally impose tariffs or other trade restrictions to protect U.S. industries from "unfair trade practices" of foreign countries.

The process has also been used to place tariffs on Chinese imports into the U.S.

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Vietnam has been on Washington's watch list of currency manipulators because of its trade surplus with the U.S., a large current-account surplus and a perception that its central bank has been actively buying foreign currency.

Vietnam's central bank governor Le Minh Hung said on Friday that his country "has not intended and will not intend to use monetary policies in general and exchange rates in particular to create unfair competitive advantage in international trade."

"We will continue to maintain exchange rate stability and keep inflation under control," Hung told a news briefing after meeting with his Southeast Asian counterparts.

Vietnam's trade surplus with the U.S., its largest export market, widened to $37.7 billion in the first eight months of this year from $29.8 billion in the same period last year, according to Vietnam's customs data.

Earlier in June, the U.S. also announced "Section 301" investigations into digital services taxes considered by 10 of its trading partners, including the European Union, Brazil and India.

(With input from Reuters)