Boeing Co and Vietnam Airlines on Monday agreed to negotiate the sale of eight more 787-10 Dreamliners and eight 777-8X aircraft, a move hailed by U.S. and Vietnamese officials as a sign of strengthening trade ties between the two former enemies.

U.S. Deputy Commerce Secretary Bruce Andrews told Reuters the Boeing aircraft sales reflected "an important dimension of a growing relationship" and said both U.S. and Vietnamese officials were committed to further expanding trade.

"There is a huge amount of opportunity for American companies in Vietnam," Andrews said before a ceremony marking the signing of a memorandum about expanding business ties and Boeing's delivery of the first 787 to Vietnam Airlines.

The event - held in the shadow of the airplane - included Nguyen Phu Trong, general secretary of the Vietnamese Communist party, who is also due to meet with President Barack Obama during a landmark visit two decades after normalization of ties between the United States and Vietnam, and 200 other U.S. and Vietnamese officials and industry executives.

Andrews said negotiators for the United States, Vietnam and 10 other countries were working to ensure that the high-standard Trans-Pacific Partnership (TPP) opened key aerospace, manufacturing and other markets in Vietnam to U.S. firms.

"That's one of the great benefits that will come from TPP," he said, calling Vietnam a key partner in Washington's strong and growing relationships in the Asia region.

Vietnam Airlines Chairman Pham Viet Thanh said a striking video of a near-vertical takeoff by the company's first 787 had been viewed 12 million times on the Internet, and his company looked forward to expanding its business with Boeing.

U.S. Transportation Secretary Anthony Foxx said the agreement between Boeing and Vietnam Airlines was "a milestone in our efforts to deepen our ties with Vietnam through bilateral trade," adding that he hoped to experience such a dramatic takeoff one day.

Foxx cited ongoing efforts to facilitate direct flights between Vietnam and the United States and continued cooperation on aviation safety.

John Wojick, Boeing senior vice president for global sales and marketing, said the agreement signed on Monday still needed work, but could include eight more 787 aircraft for Vietnam, adding to the 19 already on order.

Boeing had also offered Vietnam eight 777-8X aircraft, which the company expects to unveil at the end of the decade, he said.