US food safety officials have taken steps to ban the use of trans fats, saying they are a threat to health.

Trans fats, also known as partially hydrogenated oils, are no longer "generally recognised as safe", said the Food and Drug Administration (FDA).

The regulator said a ban could prevent 7,000 deaths and 20,000 heart attacks in the US each year.

The FDA is opening a 60-day consultation period on the plan, which would gradually phase out trans fats.

"While consumption of potentially harmful artificial trans fat has declined over the last two decades in the United States, current intake remains a significant public health concern," FDA Commissioner Margaret Hamburg said in a statement.

"The FDA's action today is an important step toward protecting more Americans from the potential dangers of trans fat."

'Industrially produced ingredient'

If the agency's plan is successful, the heart-clogging oils would be considered food additives and could not be used in food unless officially approved.

The ruling does not affect foods with naturally occurring trans fats, which are present in small amounts in certain meat and dairy products.

Foods containing trans fat Some processed baked goods such as cakes, cookies, pies

Microwave popcorn, frozen pizza, some fast food

Margarine and other spreads, coffee creamer

Refrigerator dough products such as cinnamon rolls Source: US Food and Drug Administration

Artificial trans fats are used both in processed food and in restaurants as a way to improve the shelf life or flavour of foods. The fats are created when hydrogen is added to vegetable oil, making it a solid.

Nutritionists have long criticised their use, saying they contribute to heart disease more than saturated fat.

Some companies have already phased out trans fats, prompted by new nutritional labels introduced in 2006 requiring it to be listed on food packaging.

New York City and some other local governments have also banned it.

But trans fats persist primarily in processed foods - including some microwave popcorns and frozen pizzas - and in restaurants that use the oils for frying.

According to the FDA, trans fat intake among Americans declined from 4.6g per day in 2003 to around 1g per day in 2012.

The American Heart Association said the FDA's proposal was a step forward in the battle against heart disease.

"We commend the FDA for responding to the numerous concerns and evidence submitted over the years about the dangers of this industrially produced ingredient," said its chief executive, Nancy Brown.

Outgoing New York Mayor Michael Bloomberg, who led the charge to ban trans fats in that city, said the FDA plan "deserves great credit".

"The groundbreaking public health policies we have adopted here in New York City have become a model for the nation for one reason: they've worked," he said.