(Reuters) - An environmental group on Thursday sued the U.S. government over its approach to examining the harm caused by ageing offshore oil and gas infrastructure, citing the risks delayed decommissioning poses to people and the environment.

The Center for Biological Diversity filed the lawsuit against the U.S. Interior Department in federal district court in Washington D.C. for "its ongoing failure to examine the harms from offshore oil and gas drilling infrastructure the oil industry has not decommissioned," the group said in a press release.

The Interior Department has not examined the harms of unplugged wells and idle platforms to the environment, the environmental group said.

When a company signs a lease for offshore oil or gas exploration or production, that initial agreement includes the process of decommissioning the well, according to the Bureau of Ocean Energy Management.

But as of June 2023, more than 2,700 wells and 500 platforms were overdue for decommissioning in the Gulf of Mexico, according to the U.S. Government Accountability Office.

The Department of Interior declined to comment.

Old oil and gas infrastructure must be dismantled and disposed of by plugging wells and removing platforms to prevent damage to the environment.

The group said the government's current approach violates the National Environmental Policy Act - which requires federal agencies to assess the environmental effects of proposed actions before decision-making - because the government has not adequately assessed the harm caused by delayed decommissioning.

The lawsuit seeks to force the Interior Department to conduct a new analysis that would better protect people, wildlife and the Gulf environment, the Center for Biological Diversity said in a statement.

Last month, Texas, Louisiana and Mississippi sued the U.S. government to block the Biden administration's proposed rule that would require the offshore oil and gas industry to provide nearly $7 billion in financial assurances to cover costs of dismantling old infrastructure.

The U.S. Gulf of Mexico accounts for the majority of U.S. offshore oil production, and produces roughly 1.8 million barrels per day of oil, according to the last government figures, about 14% of total U.S. output.