Another draft rule places limits on misleading advertising that attempts to show some tobacco products are less harmful than others, such as "tar-free" or "light," without providing evidence these claims actually make products safer.

The guidelines are part of the U.S. Food and Drug Administration's enforcement of a 2009 law that gives it broad authority to oversee the manufacturing and marketing of cigarettes and other tobacco products.

"Tobacco products, in this country at least, are the only mass-consumed products that consumers don't know what's in them," Dr. Lawrence Deyton, director of the FDA's Center for Tobacco Products, told reporters.

"Today, we are ending that era."

Some 8 million Americans have smoking-related illnesses, and as many as 443,000 Americans die each year from smoking-related causes such as lung cancer. Smoking is estimated to be the No. 1 preventable cause of illness and death in the United States, and contributes about $96 billion each year to health care costs.

The guidelines would force companies to tell the FDA whether their products contain any of 20 harmful or potentially harmful ingredients found in tobacco or tobacco smoke, and the amount of each.

The ingredients won't go on the packaging; rather, the FDA would compile information for each product and provide it to the public by April 2013. The FDA said it hasn't yet decided how it will present the information.

These 20 chemicals are the easiest to test for immediately, but the FDA will later make companies provide information for a full list of 93 chemicals.

Deyton, head of the FDA's tobacco center, said most people are aware of the dangers of smoking in general, but may not know specifically which chemicals in tobacco are harmful, and why.

For example, ingesting carbon monoxide - produced any time you burn something, and present in tobacco smoke - is known to increase the risk of heart disease and lung disease, the FDA said.

Besides informing the public, regulators said they hope the rules would encourage tobacco companies like Lorillard Inc and Altria Group, parent of Philip Morris USA, to make their products safer and less addictive.

Representatives from the companies could not be immediately reached for comment.

The announcement comes only a month after the government suffered a blow in court in trying to enforce another tobacco law that requires companies to put large graphic warnings on cigarette packaging. A U.S. District Court judge sided with the companies and ruled the labels were unconstitutional. The United States is appealing the decision.

The second draft rule requires FDA approval for companies to sell products they claim to be less harmful than typical tobacco products, known as modified risk tobacco products.

The companies must submit scientific studies and analyses to the FDA in order to prove their tobacco products actually benefit public health, or reduce harm.

To counter a decline in smoking in the United States, cigarette makers have focused on smokeless tobacco and other "modified risk" products.

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