Image caption The new health labels include images of individuals with heart disease and rotten teeth

Five tobacco companies have sued the US Food and Drug Administration (FDA) over a new law that would force them to place graphic health warnings on their cigarette packets.

The firms argue the plan violates their constitutional right to free speech, as it requires firms to promote the government's anti-smoking message.

The FDA has not commented on the lawsuit.

The new warnings will be required on cigarette packs from September 2012.

'Depressed, afraid'

RJ Reynolds Tobacco, Lorillard Tobacco, Commonwealth Brands, Liggett Group and Santa Fe Natural Tobacco said they filed their suit against the FDA late on Tuesday in an effort to delay enforcement of the new law.

RJ Reynolds brands include Camel and Winston, while Lorillard brands include Newport and True.

In their 41-page complaint, the five companies say the new labels would illegally force them to make consumers "depressed, discouraged and afraid" to buy their products.

"The government can require warnings which are straightforward and essentially uncontroversial, but they can't require a cigarette pack to serve as a mini-billboard for the government's anti-smoking campaign," Floyd Abrams, a lawyer representing the cigarette makers, said in a statement.

He added that the new labels would violate the companies' free-speech rights under the first amendment to the constitution.

The 2009 Family Smoking Prevention and Tobacco Control Act requires such labels to cover the top half of the front and back sides of cigarette packages and 20% of the printed advertising.

In June, Health Secretary Kathleen Sebelius said the new labels could deter young people from starting to smoke and give adult smokers a new incentive to quit.

Cigarette makers lost a similar suit last year in a US district court in Kentucky when a judge said the FDA could move ahead with forcing the companies to use the new labels, which include images of dead bodies, diseased lungs and rotten teeth.

That ruling is currently pending before the Sixth Circuit Court of Appeals.

One of the biggest US tobacco firms, Altria - parent company of Philip Morris and maker of Marlboro cigarettes - has not joined in any of the legal action against the FDA.

More than 220,000 people in the US are expected to be diagnosed with lung cancer in 2011, according to the American Cancer Society.

Tobacco use is estimated to be responsible for 443,000 deaths in the US each year.