The Food and Drug Administration said cartridge-based e-cigarettes in flavours "other than tobacco or menthol" would be illegal unless they receive specific authorization from the government.
The US government on Thursday announced it would soon ban most flavoured e-cigarettes as it tries to curb a rising tide of youth vaping, but stopped short of the full ban promised in September by President Donald Trump.
The Food and Drug Administration said cartridge-based e-cigarettes in flavours "other than tobacco or menthol" would be illegal unless they receive specific authorisation from the government.
Companies that do not cease making and selling such cartridges within 30 days will face punishment, the FDA said.
"The United States has never seen an epidemic of substance use arise as quickly as our current epidemic of youth use of e-cigarettes," Health Secretary Alex Azar said in a statement.
Azar said prioritising flavours most widely used by children would ensure e-cigarettes were a potential "off-ramp" for adult smokers but not an "on-ramp" to nicotine addiction for youngsters.
"We will not stand idly by as this crisis among America's youth grows and evolves, and we will continue monitoring the situation and take further actions as necessary," he added.
The 2019 National Youth Tobacco Survey shows that more than five million US middle and high school students are e-cigarette users, with nearly one million using daily.
"Additional data from another federal survey further underscore that youth are particularly attracted to e-cigarette flavours such as fruit and mint, much more so than tobacco or menthol-flavoured e-cigarettes," said the Department of Health and Human Services.
The flavour ban will exempt large, tank-based vaping devices, however, which are primarily sold in vape shops that cater to adult smokers.