President-elect Donald Trump on Thursday called for expanding the United States’ nuclear deterrent, hours after Russian President Vladimir Putin urged his nation to strengthen its strategic nuclear forces.

“The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes,” Trump tweeted, a reversal from the Obama and previous administration’s push for reductions in the nuclear arsenal and further arms control negotiations with Russia.

Meanwhile, Putin reportedly said in a speech earlier in the day, “We need to strengthen the military potential of strategic nuclear forces, especially with missile complexes that can reliably penetrate any existing and prospective missile defense systems,” adding that his country “must carefully monitor any changes in the balance of power and in the political-military situation in the world, especially along Russian borders, and quickly adapt plans for neutralizing threats to our country.”

The Kremlin for years has said the ballistic missile defense system the United States is deploying in Romania and Poland is a threat to Russian security and a potential trigger for a new arms race.

Both the U.S. and Russia are currently in good standing under the New Strategic Arms Reduction Treaty (New START), which requires each by February 2018 to cap their nuclear arsenals at 700 deployed ICBMs, submarine-launched ballistic missiles, and heavy bombers; 1,550 fielded strategic warheads; and 800 deployed and nondeployed long-range launchers.

These limits are set to expire in 2021, leaving Trump to decide whether to negotiate a new arms control treaty, extend New START for five additional years (an option allowed under the accord), or abandon this form of bilateral arms control. In any case, the Russian government under Putin has not demonstrated much appetite for further nuclear arms control, particularly in light of the currently icy relationship between the two countries.

In the meantime, the U.S. plans to spend $1 trillion over the next 30 years to modernize all three legs of the nuclear triad, a cost that arms control advocates and many lawmakers criticize as already being excessive. However, it remains unclear whether Trump has a specific plan in mind for augmenting the U.S. nuclear capability, and therefore how it would impact spending levels.

Weeks before taking office, Trump has already used Twitter to excoriate what he sees as excessive defense spending for the Air Force’s F-35 fighter jet and Air Force One.

Trump’s transition team did not respond by press time to a request for specifics on the expanded nuclear capabilities he suggested.

Miles Pomper, a senior fellow at the James Martin Center for Nonproliferation Studies, said by email t is not clear what Trump meant by an expanded nuclear capability. “It seems to have been a reaction to Putin’s comments earlier today on devising nukes to penetrate US missile defenses—a longstanding Russian effort,” he said.

“The comments are frankly pretty strange given his apparent desire otherwise to avoid confrontation with Russia that this is the area in which he would choose confrontation,” Pomper said. “Neither country needs to build more nuclear weapons.” Instead, they should stick to New START and address tactical nuclear weapon issues, he said.

In May, the Congressional Research Service said that while the United States has roughly 760 nonstrategic nuclear weapons – roughly 200 of which are deployed in Europe – Russia is believed to have between 1,000 and 6,000 nonstrategic nuclear warheads in its arsenal.

James Acton, co-director of the Nuclear Policy Program at the Carnegie Endowment for International Peace, tweeted in response to Trump’s post, “PEOTUS appears to want a larger arsenal & new nuclear capabilities. Neither is likely to enhance deterrence.”

A number of arms control advocates concurred in a rush of posts on Twitter, while others came down on Trump’s side: “An absolutely perfectly sensible point to make,” tweeted James Carafano, a national security expert at the Heritage Foundation who is now a member of Trump’s transition team.