By Laura Zuckerman

(Reuters) - The U.S. Department of Energy on Friday said it would be unable to meet a deadline to remove drums of nuclear waste from Los Alamos National Laboratory in New Mexico because of safety concerns tied to the radiological materials.

New Mexico officials asked federal officials to remove 3,706 cubic meters of waste from a mesa on the Los Alamos complex, out of a concern that wildfires could reach the material.

Much of that nuclear waste has been removed, and the U.S. Department of Energy had agreed to transfer the rest of it to a Texas facility by June 30.

But those shipments have been put on hold due to concerns about the chemical stability of the mixture in the containers that have arisen since it was discovered a drum from the federal Los Alamos National Laboratory may be behind a radiological leak at a repository near Carlsbad, New Mexico.

“As we work to assess the conditions of the transuranic waste program at the (Los Alamos) lab, we have decided to halt further shipments until we can reassure the public that it is safe to do so,” David Klaus, an Energy Department secretary for management and performance, said in a statement.

New Mexico Environment Department Secretary Ryan Flynn said in a statement he was “disappointed, but not surprised” by the decision.

The backup of nuclear waste at Los Alamos has been worsened by the shutdown of the Waste Isolation Pilot Plant in Carlsbad, the only facility of its kind in the United States, where material from Los Alamos had been sent.

A drum from Los Alamos is suspected in a radiation leak on Feb. 14 at the underground repository for so-called transuranic waste, which consists of tools, rags and other debris contaminated with radioisotopes such as plutonium from U.S. nuclear labs.

Government investigators believe a chemical reaction between organic kitty litter used as a new absorbent and nitrate salts in the radiological waste likely caused the drum to breach and eject materials onto a container nearby.

Also on Friday, officials at the Waste Isolation Pilot Plant said an ongoing investigation and cleanup tied to the Feb. 14 radiation release and an accident the week before that saw a truck catch fire would prevent the facility from setting firm deadlines for sealing off two vaults that collectively hold 368 drums of nuclear refuse from Los Alamos.

(Reporting by Laura Zuckerman in Salmon, Idaho; Editing by Alex Dobuzinskis and Jeremy Laurence)