By JULIE PACE
AP White House Correspondent
WASHINGTON (AP) -- 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 asses 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."
A U.S.-backed missile shield in Eastern Europe has been another source of tension between Washington and Moscow. Russia argues the system is a threat, while U.S. and NATO officials say it's meant to deter Iran from targeting Europe.
The state of the U.S. nuclear arsenal was rarely addressed during the presidential campaign. To the extent it was, Trump showed faint understanding of its details. During a Republican primary debate, he appeared unfamiliar with the concept of a nuclear triad, the Cold War-era combination of submarines, land-based missiles and strategic bombers for launching nuclear attacks.
Trump's vanquished campaign rival Hillary Clinton repeatedly cast the Republican as too erratic and unpredictable to have control of the nation's nuclear arsenal.
The president-elect's transition website says he "recognizes the uniquely catastrophic threats posed by nuclear weapons and cyberattacks," adding that he will modernize the nuclear arsenal "to ensure it continues to be an effective deterrent."
Trump has spent the week at Mar-a-Lago, his South Florida estate, meeting advisers and interviewing candidates for a handful of Cabinet positions that remain unfilled. On Wednesday, he met with Pentagon officials and the CEOs of Boeing and Lockheed Martin, companies with lucrative government contracts.
Since winning the election, Trump has complained about the cost of Boeing's work on two new Air Force One planes and Lockheed's contract for F-35 fighter jets. Following the meetings, both CEOs said they had discussed lowering costs of the projects with the president-elect.
On Thursday, Trump pitted the two companies against each other on Twitter. "Based on the tremendous cost and cost overruns of the Lockheed Martin F-35, I have asked Boeing to price-out a comparable F-18 Super Hornet!" he tweeted.
Boeing spokesman Todd Blecher said Thursday, "We have committed to working with the president-elect and his administration to provide the best capability, deliverability and affordability." Lockheed declined to comment.
Trump's tweet came after the close of trading on Wall Street. But in after-hours dealings, shares of Bethesda, Maryland-based Lockheed Martin Corp. fell 2 percent, while Chicago-based Boeing Co.'s stock rose 1 percent.
Boeing and Lockheed are also among the companies pursuing a contract for replacing Minuteman missiles in the U.S. nuclear arsenal. Spokespeople for the two companies declined to comment on whether that contract came up during Trump's meetings with their CEOs.
The president-elect was also building up his White House staff, announcing Thursday that campaign manager Kellyanne Conway would serve as a counselor. The move will put Conway in close proximity to the president, though she is also expected to remain a visible presence promoting Trump's agenda in the media.
Trump also announced veteran Republican operatives Sean Spicer as his press secretary and Jason Miller as communications director. Hope Hicks, Trump's long-serving campaign spokeswoman, is also joining the White House in a senior communications position.
Associated Press writers Lynn Berry and Joan Lowy in Washington and Jonathan Lemire in Palm Beach, Florida, contributed to this report.
Follow Julie Pace at http://twitter.com/jpaceDC