(CNN) The US Food and Drug Administration recently conducted a surprise inspection of e-cigarette maker Juul's corporate headquarters in San Francisco, seizing thousand of documents, many of which relate to the company's sales and marketing practices.

The agency said the inspection, completed Friday, is part of its "ongoing efforts to prevent youth use of tobacco products, particularly e-cigarettes."

In September, the FDA requested five major e-cigarette manufacturers, including Juul, explain how they plan to combat the use of their products by minors. The FDA said it was looking into potential steps to eliminate the sale of flavored products and unveiled a public education campaign about e-cigarettes.

On Tuesday, the FDA said it inspected several of Juul's contract manufacturing facilities earlier in the year.

"The new and highly disturbing data we have on youth use demonstrates plainly that e-cigarettes are creating an epidemic of regular nicotine use among teens," FDA spokesman Michael Felberbaum wrote in an email. "It is vital that we take action to understand and address the particular appeal of, and ease of access to, these products among kids."

In a statement on its website on Tuesday, Juul Labs said that it is "committed to preventing underage use, and we want to engage with FDA, lawmakers, public health advocates and others to keep Juul out of the hands of young people."

The statement adds that the company's meetings with the FDA were "constructive" and allowed for a "transparent dialogue," and gave Juul the chance to show the agency its age-verification protocols.

The company said that it has released over 50,000 pages of documents to the FDA since April.

"We look forward to presenting our plan to address youth access in the 60-day time frame as outlined by FDA. We want to be part of the solution in preventing underage use, and we believe it will take industry and regulators working together to restrict youth access," the statement said.

Juul dominates the e-cigarette market

E-cigarettes work by heating a pure liquid called e-juice -- composed of flavorings, propylene glycol, glycerin and often nicotine -- until it vaporizes. Juul's e-cigarettes come in sweet fruit flavors, as well as traditional flavors such as tobacco and mint. The company has drawn criticism for its device's resemblance to a USB device, which is easy to hide.

Juul sales grew 641% from 2016 to 2017, according to an analysis of the sales data published Tuesday in the journal JAMA

British American Tobacco led the US e-cigarette market into 2017, the researchers said. By December 2017, Juul held the greatest share of the US market; it sold 2.2 million devices in 2016, and by 2017, that number rose to 16.2 million.

"It was not designed to look like a USB device. It was not designed to be hid by kids. This is a product that was designed by smokers for adult smokers," Juul Chief Administrative Officer Ashley Gould told CNN this year

The product was designed for adult smokers trying to make the switch from combustible cigarettes, the company said, but data showed that it had a strong appeal among kids.

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An April survey of young Juul users by Truth Initiative, a nonprofit tobacco control organization, found that 63% did not know that the product contained nicotine. The company has added larger warning labels spelling out that the product contains nicotine.

"It's been devastating to us," Gould said of youth Juul use. "This is not a product for youth. It's a product for adult smokers.

"We understand and have heard reports that youth may find the design attractive. And we are committed to combating underage use of the product."