(Reuters) - Sixteen attorneys general and a coalition of six environmental groups separately sued the Trump administration on Tuesday in Washington D.C. federal appeals court over a rule that would allow the transportation by rail of explosive liquefied natural gas, arguing that the measure would be dangerous and could destroy cities.

In this first lawsuit, the Sierra Club, the Center for Biological Diversity and other groups petitioned the U.S. Court of Appeals for the D.C. Circuit over the U.S. Department of Transportation rule scheduled to take effect next week, alleging that it violates the Hazardous Materials Transportation Act.

A lawsuit filed shortly thereafter by Democratic attorneys general from Maryland, California, New York and 13 other states also alleges violations of the Administrative Procedure Act and the National Environmental Policy Act.

The DOT's Pipeline and Hazardous Materials Safety Administration (PHMSA) published on July 24 a finalized version of the new measure, an amendment of the Hazardous Materials Regulations that allows for the bulk nationwide transportation of liquefied natural gas in rail tank cars for first time ever, said Earthjustice attorney Jordan Luebkemann. The rule is slated to take effect on Aug. 24.

To transport natural gas, the substance must be converted to liquid form. Liquefied natural gas is flammable, odorless, and highly hazardous. Derailments of less explosive substances like crude oil have caused serious explosions, the environmental groups say.

In 2013, parts of the Canadian town of Lac Megantic was destroyed following the derailment of train carrying crude oil.

Environmental plaintiffs, represented by Earthjustice attorneys, say the measure is "dangerous" given the explosive nature of the fuel they would transport.

"It would only take 22 tank cars to hold the equivalent energy of the Hiroshima bomb," said Earthjustice attorney Jordan Luebkemann in a statement.

The attorneys general intend to argue in their lawsuit that PHMSA failed to evaluate the environmental impacts of the rule. They will also argue that it "lacks the necessary safety requirements to minimize the risk to public safety associated with transporting LNG by rail," the AGs said in a statement.

The Trump administration rule would help natural gas drillers export the fuel and benefit rail operators rebound who have suffered as coal output has fallen.

PHMSA has said that a specially-built rail car is designed to handle super-cooled liquids like liquified natural gas. Still, attorneys general from 16 states in January opposed the regulation, arguing that potential leaks from the shipments pose risks of explosions to residents.

PHMSA does not comment on litigation.

The cases are is Sierra Club at al. v. United States Department of Transportation et al., U.S. Court of Appeals for the District of Columbia, No. N/A.

For Sierra Club at al.: Aaron Stemplewicz, Bradley Marshall and Jordan Luebkemann of Earthjustice

State of Maryland et al. v. United States Department of Transportation et al., U.S. Court of Appeals for the District of Columbia, No. N/A.

For State of Maryland et al.: Brian Frosh of the Office of the Attorney General of Maryland