Washington DC - President Donald Trump's administration on Thursday night fired and then rehired more than 300 staffers working for the National Nuclear Security Administration (NNSA), which oversees the US nuclear stockpile.

Sources close to the matter told CNN that more than 300 staffers at the NNSA were let go on Thursday night as part of massive layoffs in the Department of Energy, before being quickly rehired.

A spokesperson for the Department of Energy disputed the claim, telling CNN that less than 50 people – mostly administrative staff – had been dismissed.

According to the leaks, many of the fired employees oversaw the construction of nuclear weapons and even inspected them to make sure they were built safely.

Donald Trump Trump drops shocking tariff rates on cars, semiconductors, and pharmaceuticals

"No one has taken anytime to understand what we do and the importance of our work to the nation’s national security," one source was cited as telling CNN.

The NNSA employs about 1800 people across its various US facilities, many of them probationary workers who have significantly fewer rights and job protections than those with full-time permanent contracts.

The Trump administration used the excuse of poor performance to justify the firings, but sources expect that most of the employees who were terminated would return.

Meanwhile, the firings have caused a stir among Congress members, who are concerned that Trump's ongoing cuts and gutting of the civil service could destroy nuclear deterrence.

"Congress is freaking out because it appears DOE didn’t really realize NNSA oversees the nuclear stockpile," a source told CNN.

"The nuclear deterrent is the backbone of American security and stability – period. For there to be any even very small holes poked even in the maintenance of that deterrent should be extremely frightening to people."