The popular e-cigarette brand Juul Labs is under investigation by the Massachusetts attorney general, who is concerned the company is targeting minors.

During a livestreamed press conference on Tuesday, Attorney General Maura Healey said Juul's products have become a hit among middle and high school students. The company offers its nicotine cartridges -- which contain as much nicotine as a pack of cigarettes -- in flavors like fruit medley and mango. And its rechargeable smoking devices, which resemble a flash drive, come in colorful "skins," she said.

The company's growing popularity among minors underscores "why we need to act as a state and why, frankly, I'm sounding the alarm today," she said.

Healey's office is investigating whether Juul violates state law by failing to prevent minors from buying its products. Investigators also want to determine whether Juul intentionally markets its products to teens and tracks underage use of its products. It also wants to know whether the company is properly monitoring retailers to ensure they are verifying customers are older than 21, as state law requires.

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The San Francisco company holds about two thirds of the vaping market and it is reportedly valued at $15 billion -- roughly the same as ridehailing company Lyft. Its products are so pervasive that "juuling" is a verb synonymous with vaping.

Healey's office also sent cease-and-desist letters to Direct Eliquid LLC, which operates directeliquid.com and buyjuul.com, and Eonsmoke, LLC, which runs eonsmoke.com, ordering them to stop selling e-cigarette products without proper age verification requirements mandated by the state.

In April, the US Food and Drug Administration announced a nationwide crackdown on the sale of e-cigarettes to minors. The FDA also asked Juul to provide any documents about its product marketing and research into the health effects of its products.

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A spokesperson for Juul Labs told CNNMoney it complied with the FDA's request and welcomes the opportunity to work with the Massachusetts Attorney General.

"We too, are committed to preventing underage use of Juul," Matt David, the company's chief communications officer at Juul Labs, said in a statement. "We utilize stringent online tools to block attempts by those under the age of 21 from purchasing our products, including unique ID match and age verification technology."

Earlier this week, Wired reported Juul Labs has been hit with at least three lawsuits since April alleging that deceptive marketing led consumers to believe its products were safe. The company said it "does not believe the cases have merit and will be defending them vigorously."