(CNN) — Fliers heading to Thailand may have fresh cause for concern after the country's airlines were hit with restrictions by U.S. aviation authorities.

The Federal Aviation Administration announced Tuesday that it was downgrading Thailand's aviation safety rating to Category 2 because the country did not comply with international standards.

The decision means Thai airlines will be banned from opening new routes to the United States or expanding existing ones.

While none currently operate direct routes to the U.S., the FAA's downgrades are often matched by other global aviation authorities, raising the prospect of restrictions on routes to Europe or East Asia.

Shares in several Thai airlines fell following the news.

In stripping it of the Category 1 rating it received in 1997, the FAA said Thailand's civil aviation authority failed to meet "minimum international standards."

Category 1 means that the country complies with International Civil Aviation Organization standards.

The ICAO, a United Nations agency, "red flagged" Thailand in June over safety concerns, listing it alongside Angola, Botswana, Djibouti, Eritrea, Georgia, Haiti, Kazakhstan, Lebanon, Malawi, Nepal, Sierra Leone and Uruguay.

The ICAO's concerns have previously led to restrictions on new airline routes linking Thailand with China, South Korea and Japan.

Safety reassurances

In response to the FAA's decision, Thailand's prime minister, Prayut Chan-o-cha, ordered a swift overhaul of his country's aviation systems.

He acknowledged the setback could undermine confidence in the military leadership that seized power in a 2014 coup.

"Therefore, all must join hands to bring peace to the country," he said, according to the Bangkok Post . "Don't try to pick a quarrel, because doing so will not lead us out of crisis."

The country's leading international carrier, Thai Airways, issued a statement defending its safety record.

It said the decision would have no impact on its business or customers as it ceased its only U.S. destination flight, to Los Angeles, in October, although it continues to operate code share connections.