The drop comes after warnings from the travel industry about the negative impact of increased travel restrictions from the Trump administration.

The US announced new visa restrictions for six mainly Muslim countries and banned laptops on some flights earlier this year.

It reversed the laptop policy in July.

The US Commerce Department on Thursday defended the administration's record, pointing to a rise in travel-related spending, which increased 3% year-on-year in the first half of 2017.

"This proves that international travellers know that the safety enhancements introduced by the Trump administration are far more important than the processing inconveniences from them," said Commerce Department Secretary Wilbur Ross.

Trump slump?

The number of international visitors to the US has risen steadily from 2009, peaking in 2015 at 77.5 million, according to the National Travel and Tourism Office.

Visits fell 2.4% in 2016, with Canada and Mexico accounting for just over half of the travellers.

In the first three months of 2017, about 15.8 million people visited the US from foreign countries, down about 4% year-on-year, the office reported.

The number of visitors from Canada increased 5% year-on-year to 4.6 million during the quarter.

But visits from the next four major tourist markets - Mexico, the UK, Japan and Germany - were down in the January through March period.

The number of travellers from Mexico fell by 7.1% to 3.9 million.

UK visits slid 15.5% to about 774,800 and the number of Japanese travellers slipped 2.1% to 884,900.

The number of German visitors shrank almost 12% to about 360,000.

Total European visitor numbers fell by 10% to 2.6 million.

The number of visitors from the Middle East plunged 25% year-on-year to 204,000.

Analysts had warned that Trump administration policies were hurting travel, while surveys suggest opinions of the US have deteriorated.

The US was the only country among major destinations where long-haul bookings declined in the first half of the year, ForwardKeys reported in June.

Emirates had cut back its routes to the US, citing fewer passengers under the new rules.

But Emirates president Tim Clark said this month the airline might restore some of the routes it cut in in the next six to nine months.