WASHINGTON — President-elect Donald Trump on Thursday abruptly called for the United States to “greatly strengthen and expand its nuclear capability” until the rest of the world “comes to its senses” regarding nuclear weapons.

His comments on Twitter came hours after Russian President Vladimir Putin said strengthening his country’s nuclear capabilities should be a chief military objective in the coming year. The president-elect’s statement also followed his meetings a day earlier with top Pentagon officials and defense contractors.

Trump, who is spending the holidays at his palatial private club in Florida, did not expand on the actions he wants the U.S. to take or say why he raised the issue Thursday.

Spokesman Jason Miller said the president-elect was referring to the threat of nuclear proliferation “particularly to and among terrorist organizations and unstable and rogue regimes.” Miller said Trump sees modernizing the nation’s deterrent capability “as a vital way to pursue peace through strength.”

If Trump were to seek an expansion of the nuclear stockpiles, it would mark a sharp shift in U.S. national security policy. President Barack Obama has made nuclear non-proliferation a centerpiece of his agenda, calling in 2009 for the U.S. to lead efforts to rid the world of nuclear weapons — a goal he acknowledged would not be accomplished quickly or easily.

Still, the U.S. has been moving forward on plans to upgrade its aging nuclear arsenal. Earlier this year, Defense Secretary Ashton Carter said the Pentagon planned to spend $108 billion over the next five years to sustain and improve its nuclear force.

The U.S. and Russia hold the vast majority of the world’s nuclear weapons. In 2010, the two countries signed the New START treaty capping the number of nuclear warheads and missile launchers each country can possess. The agreement is in effect until 2021 and can be extended for another five years.

Thomas Karako, senior fellow at the Center for Strategic and International Studies, said the last comprehensive review of the U.S. nuclear force — which was conducted during Obama’s first term — occurred against the backdrop of efforts to reset relations between Washington and Moscow. The relationship has since deteriorated, with Obama and Putin clashing over Russia’s provocations in Ukraine and support for Syrian President Bashar Assad.

“We need to candidly assess what the environment is and what the prospects are for Russian compliance with current treaties,” Karako said.

Trump has repeatedly called for closer relations with Russia and has spoken favorably about Putin. Democrats have questioned his ties to the Kremlin, particularly after U.S. intelligence officials assessed that Russia had interfered in the U.S. election on Trump’s behalf.

Putin addressed his country’s nuclear capabilities during an annual year-end meeting of the Russian defense ministry. He said Russia should enhance missile complexes that can “penetrate existing and future missile defense systems.”