Black-tinged lungs. A foot with amputated toes. A sickly boy in an oxygen mask.

Those graphic images are among 13 cigarette health warnings the U.S. Food and Drug Administration released Thursday as part of a proposed rule that would require the images - along with vivid descriptions - to be printed on all cigarette packaging. The agency calls it the most "significant change" to labels in 35 years and says its intention is to raise awareness about the consequences of smoking, the FDA said.

"There's a surprising number of lesser-known risks that both youth and adult smokers and nonsmokers may simply not be aware of, such as bladder cancer, diabetes and conditions that can cause blindness," FDA acting commissioner Norman "Ned" Sharpless said in a news release.

The FDA's proposed warnings, mandated by the Family Smoking Prevention and Tobacco Control Act of 2009, come years after it unsuccessfully sought to require similarly graphic labels. Those were blocked in court by big-name tobacco companies that claimed the warnings violated their First Amendment rights.

The final version of the proposed rule is due in March 2020; 15 months later, the warnings would be required on cigarette packages and in advertisements, according to the FDA.

It's unclear whether tobacco companies will oppose the newest warnings. R.J. Reynolds Tobacco said it is reviewing the FDA's proposal.

"We firmly support public awareness of the harms of smoking cigarettes, but the manner in which those messages are delivered to the public cannot run afoul of the First Amendment protections that apply to all speakers, including cigarette manufacturers," Kaelan Hollon, a spokeswoman for Reynolds American, said in a statement.

With more than 480,000 fatalities each year, cigarette smoking is the leading cause of preventable death in the United States, according to the Centers for Disease Control and Prevention. Though the habit has declined, an estimated 34 million adults still smoke - and about 16 million are battling smoking-related diseases, the CDC said.

"The new graphic warnings are a dramatic improvement over the current text-only warnings that have become stale and unnoticed," said a joint statement from leading health organizations, including the American Cancer Society, American Heart Association, American Lung Association and the American Academy of Pediatrics. "They are supported by extensive scientific evidence, and they will help the United States catch up to the 120-plus countries that have adopted this best-practice strategy to reduce tobacco use and save lives."

The proposed warning labels warn smokers that smoking cigarettes "causes COPD, a lung disease that can be fatal," "reduces blood flow to the limbs, which can require amputation" and "can harm your children."

Noel Brewer, a professor of health behavior at the University of North Carolina's Gillings School of Global Public Health, said that graphic labels have been shown to be powerful reminders about smoking risks.

Several years ago, Brewer and other researchers in North Carolina studied nearly 2,000 smokers over a four-week period and found that those exposed to warnings with graphic images on their cigarette packages were more likely to try to stop smoking than those who were not.

Brewer said even a small change in smoking habits can result in big health improvements.