"Since GAO's last 2017 report recommending that NNSA [National Nuclear Security Administration] address affordability issues for its program of work in Fiscal Year 2017, the Trump administration has moved in the opposite direction by increasing the role, types, and cost of US nuclear weapons", the release said.
In a letter to US Comptroller General and GAO chief Gene Dodaro, Markey and Feinstein asked whether the NNSA has embraced an earlier GAO recommendation to defer or cancel specific modernisation programs, the release added.
The Obama administration proposed spending $1.2 trillion to modernise the nation's nuclear arsenal.
In 2018, the Trump administration issued a Nuclear Posture Review that expanded the plan - and presumably the cost - by developing two new nuclear warheads, including one with less powerful explosive capacity for submarine-launched ballistic and cruise missiles.
The lawmakers' letter asked the GAO to compare projected modernisation costs indicated by the White House's proposed 2021 budget to projections in place prior to the administration's Nuclear Posture Review.
The proposed 2021 budget calls for a 25 percent increase in spending for nuclear modernisation over 2020 levels, according to the release. US Secretary of Defence Mark Esper has said that the Department's 2021 budget request offers solutions to the modernisation of the US nuclear arsenal "in response to Russia's expanding inventory".