Richmond, Va. - A trade group is encouraging convenience stores and gas stations not to sell electronic cigarettes to minors, according to a position statement obtained by The Associated Press.

The National Association of Convenience Stores' new position states that, as a best practice, e-cigarettes should be treated just like other age-restricted tobacco products. The move was communicated to its members on Thursday.

Electronic cigarettes are battery-powered devices that heat a liquid nicotine solution, creating vapor that users inhale. The category has grown from thousands of users in 2006 to several million worldwide.

The more than 151,280 convenience stores in the U.S. accounted for nearly $540 million in e-cigarette sales in 2013, making it the largest retail channel for the products, the Alexandria, Va.-based association said.

"We're sitting on the front lines. ... It is our responsibility to make sure that children don't have access to (e-cigarettes) in the event that they are risky products and could lead to somebody starting to smoke tobacco products," Henry Armour, the industry group's president and CEO, said in an interview with the AP.

Armour's association's members check 4.5 million ID cards per day for age-restricted products. It was a founding member of the We Card program in the 1990s, which requires face-to-face ID checks for tobacco products.

The fast-growing e-cigarette industry is awaiting regulation by the Food and Drug Administration, which will likely ban sales to minors nationwide and impose other marketing and product restrictions. The agency first said it planned to assert authority over e-cigarettes in 2011 but hasn't yet. The proposed FDA regulation was submitted to the Office of Management and Budget for review in October.

In the meantime, more than two dozen states have laws prohibiting the sale of e-cigarette to minors and many of their makers of the more than 250 brands already restrict sales to those under 18. Additionally, members of Congress and public health groups have raised concerns over e-cigarette marketing and have floated legislation to ban marketing to children based on standards set by the Federal Trade Commission.

Companies vying for a stake in the electronic cigarette business are reviving the decades-old marketing tactics the tobacco industry used to hook generations of Americans on regular smokes. Those tactics, such as running TV commercials and sponsoring race cars and other events, are raising worries that e-cigarette makers could tempt young people to take up something that could prove addictive.

About 2 percent of U.S. teenage students said they'd used an e-cigarette in the previous month, according to the survey done in 2012 and released by the Centers for Disease Control and Prevention. And about 7 percent said they'd tried an e-cigarette at least once in 2012, which translates to nearly 1.8 million students. The study was based on a questionnaire filled out by nearly 19,000 students in 2011 and 25,000 students in 2012.

Health officials say the study suggests many kids are now getting a first taste of nicotine through e-cigarettes and moving on to regular tobacco products. Children, however, are still more likely to light up regular cigarettes, though teen smoking rates have dropped in the past decade.