Trump on Monday signed an order that "mandated a process to develop an 'American Iron Dome,'" a next-generation US missile defence shield against ballistic, hypersonic, cruise missile and other forms of aerial attack.
The White House said the intention was to modernise an outdated system and address a "catastrophic threat" that had become more complex as US adversaries developed new delivery systems.
But Russian Foreign Ministry spokeswoman Maria Zakharova said the plan was aimed at undermining the ability of both Russia and China to exercise nuclear deterrence.
In the sharpest Russian criticism so far of a policy announced by Trump's new administration, she said that the planned US move would hinder the prospects for talks on nuclear arms control - something that both Trump and Russian President Vladimir Putin have said they favour.
"It (the plan) directly envisages a significant strengthening of the American nuclear arsenal and means for conducting combat operations in space, including the development and deployment of space-based interception systems," Zakharova told reporters at a news briefing in Moscow.
"We consider this as another confirmation of the US focus on turning space into an arena of armed confrontation... and the deployment of weapons there.
"The indicated US approaches will not contribute to reducing tensions or improving the situation in the strategic sphere, including creating a basis for a fruitful dialogue on strategic offensive arms," she said.
The White House's Iron Dome statement did not refer to strengthening the US nuclear arsenal, but said:
"The Iron Dome will further the goals of peace through strength. By empowering the United States with a second-strike capability, the Iron Dome will deter adversaries from attacks on the homeland."
Trump and Putin have both said they would like to meet face-to-face to discuss a range of issues, including the Ukraine war, but Moscow says it has yet to receive any signals from the US on when and where such an encounter could take place.
