Seven US conservation groups on Thursday filed a lawsuit against the Environmental Protection Agency, accusing the government of failing to regulate the use of toxic lead bullets in hunting.

Lead bullets have been shown to fragment upon impact, leaving bits behind in carcasses that other animals scavenge. The practice can cause lead poisoning in species such as the endangered California condor, eagles, swans and more.

A petition by 100 environmental groups to the EPA in March, asking for the agency to regulate the components of ammunition used in hunting under the Toxic Substances Control Act, was refused amid strong opposition by gun rights groups.

"The EPA has the ability to immediately end the unintended killing of eagles, swans, loons, condors and other wildlife," said Jeff Miller with the Center for Biological Diversity, one of the seven groups filing the latest suit.

"Unfortunately, the agency refuses to address this needless poisoning. We've removed toxic lead from gasoline, paint and most products exposing humans to lead poisoning; now it's time to do the same for hunting ammunition to protect America's wildlife."

The Center says millions of birds and other wildlife -- 130 species in all -- are poisoned each year from scavenging big game left behind by hunters who used lead bullets.

"Wildlife hospitals across the country see a dramatic rise in lead-poisoned eagles and other raptors during hunting season each fall," said Louise Shimmel, executive director of the Cascades Raptor Center in Oregon, another party to the suit.

"Lead poisoning is a major cause of death and injury for wildlife, and is easily preventable by taking action to prohibit lead shot."

Some hunters prefer to use copper bullets, which do not fragment like lead and are safer for the environment.

However, groups like the National Rifle Association oppose any move to ban or regulate lead in ammunition, saying it would infringe on gun rights and raise costs for hunters.

A ban on hunters' use of lead shot for killing waterfowl was passed in the United States in the early 1990s because birds were being poisoned by ingesting the pieces that fell into waterways and ponds.

But the question of whether to do the same for hunters on land has sparked a fresh political battle over gun rights and environmental protection.

More than a dozen countries in Europe have banned lead ammunition for hunting waterfowl, while Norway, the Netherlands, Denmark and Sweden are among a handful of countries that have totally banned lead bullets.

Germany, Japan and Belgium have passed limited restrictions on their use.