Published: Sep 09, 2010 6:31 PM EDT
Updated: Sep 09, 2010 3:31 PM EDT

RICHMOND, Va. (AP) - The Food and Drug Administration is lighting a fire under the electronic cigarette industry to work with the agency to legally market the devices and is cautioning other companies that their sales and manufacturing practices violate federal law.

The FDA said Thursday it sent warning letters to five companies that make e-cigarettes or components for the plastic and metal devices that heat a liquid nicotine solution in a disposable cartridge, creating vapor that the "smoker" inhales.

In the letters, the FDA said the companies are violating the Federal Food, Drug and Cosmetic Act, including unsubstantiated claims and poor manufacturing practices.

The companies receiving warning letters are: E-CigaretteDirect LLC, Ruyan America Inc., Gamucci America, E-Cig Technology Inc. and Johnson Creek Enterprises LLC.

But in a letter to the Electronic Cigarette Association, the FDA said the actions against the companies were not meant to be seen as a larger effort to ban e-cigs. The agency encouraged the industry group to work with the FDA to ensure the safety and effectiveness of the devices to help people quit smoking traditional cigarettes through usually expensive clinical trials.

The battery-powered electronic cigarettes have become the center of a fight over how risky they are compared with traditional smokes, whether they're legal and, if they are, how they should be regulated.

The FDA and public health groups have sounded the alarm, saying they contain dangerous chemicals and are being marketed to children, and the federal agency has halted shipments of e-cigarettes at ports nationwide.