Federal regulators have opened a criminal probe into e-cigarette-related lung illnesses in the United States.

There were seven deaths and 530 confirmed or suspected cases of serious illness related to vaping by late Thursday.

The Food and Drug Administration says it has no intention of prosecuting e-cigarette users, but says its criminal investigations division can help federal authorities figure out why people are getting sick.

The Centers for Disease Control and Prevention is urging people to stop vaping. But it says no one should go back to smoking tobacco cigarettes, urging smokers to get counseling or use FDA-approved products to stop smoking.

Health experts have been unable to pinpoint an exact cause of vaping-related lung illnesses, including a specific brand or ingredient in e-cigarettes. But some suspect the use of the marijuana component THC in vaping devices.

E-cigarette devices have been marketed as a safer alternative to tobacco. Federal regulators have warned the largest e-cigarette maker, JUUL, against making such claims, saying they have not been proven.

New York this week became the first state to immediately ban flavored e-cigarettes, saying the fruit and candy flavors used in vaping devices are meant to appeal to young people.

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Only tobacco and menthol flavors can be sold in New York. Michigan has also approved a ban on flavors, but it has not taken effect yet. Other states are also considering a ban. (VOA)