There are currently no non-stop flights between the two countries, despite a large market catering to tourism and visits by friends and relatives.

Vietnam Airlines JSC and Bamboo Airways have both expressed the desire to fly to the United States, but are barred from doing so until the South-east Asian nation receives the Category 1 rating.

The US officials, speaking on condition of anonymity, said the Category 1 rating should be issued in the coming weeks.

Last year, the US Federal Aviation Administration (FAA)sent a team to Vietnam to conduct a safety assessment, industry publication Aviation Week said.

The FAA did not immediately respond to a request from Reuters for comment.

Unlike Thailand, which once had a Category 1 rating and is seeking to regain it after a downgrade to Category 2, Vietnam does not hold a FAA rating.

Vietnam's rapidly growing aviation market saw traffic increase 16 per cent on average each year from 2010 to 2017, data from its civil aviation regulator shows.

Its airlines, which also include budget carriers VietJet Aviation JSC and Jetstar Pacific, are major customers of Boeing Co and Airbus SE.

Reuters - January 31, 2019