This combination of pictures created on March 17, shows U.S. President Donald Trump in the Oval Office of the White House in Washington, D.C., March 13, and Russia's President Vladimir Putin at the Kremlin in Moscow, March 13. AFP-Yonhap

U.S. President Donald Trump and Russian President Vladimir Putin agreed Tuesday on the need for cooperation on nuclear nonproliferation, raising questions over whether their potential collaboration would ultimately extend to cover North Korea's long-elusive nuclear quandary.

Trump and Putin reached the agreement during a lengthy phone call, during which Putin agreed to temporarily halt strikes on Ukrainian energy infrastructure targets in what the White House described as part of the "movement to peace."

On the nonproliferation front, the White House said the leaders discussed the "need to stop proliferation of strategic weapons and will engage with others to ensure the broadest possible application," while the Kremlin said joint efforts will be made to "establish cooperation on nuclear nonproliferation and global security."

Their agreement was keenly watched in Seoul as South Korea has been doggedly pushing for hitherto unfruitful efforts to persuade North Korea to renounce its nuclear program, which has only been advancing amid its diversification of nuclear delivery vehicles.

It came as the 2010 New Strategic Arms Reduction Treaty (New START) is set to expire in February next year unless a new deal is struck. Given the treaty is the last remaining pact limiting U.S. and Russian strategic nuclear arsenals, its absence is feared to raise risks of nuclear war.

In fact, the New START has all but ceased to operate as Putin announced the suspension of Russia's participation in the treaty in February 2023, saying that to resume treaty activities, Washington would need to stop its military support for Ukraine.

Security tensions already deepened in 2019 when the first Trump administration pulled out of the Intermediate-Range Nuclear Forces Treaty (INF), a key Cold War-era security pact, arguing Russia had failed to abide by INF obligations. The INF bans ground-based cruise and ballistic missiles with ranges from 500 to 5,500 kilometers.

Since taking office, Trump has hinted at his interest in nuclear arms control talks with Russia and China. He has repeatedly noted that during his first term, he discussed "denuclearization" with Putin, who he claimed liked the idea of "cutting way back" on nuclear weapons.

"In fact, with President Putin prior to an election result (in 2020), we were talking about denuclearization of our two countries and China would have come along," he said during his virtual participation in the World Economic Forum in late January.

Trump also said that efforts to reduce nuclear arms would have been an "unbelievable thing for the planet."

In this file photo taken on June 12, 2018 (FILES) In this file photo taken, June 12, 2018, U.S. President Donald Trump, right, and North Korea's leader Kim Jong-un shake hands following a signing ceremony during their historic U.S.-North Korea summit, at the Capella Hotel on Sentosa island in Singapore. AFP-Yonhap

"I can tell you that President Putin wanted to do it. He and I wanted to do it," he said. "We had a good conversation with China. They would have been involved."

During a press availability in February, Trump reiterated his desire to engage in nuclear arms control talks with Russia and China, while voicing hope to spend money for building nuclear weapons on "other things" that are "much more productive."

"There's no reason for us to be building brand new nuclear weapons, we already have so many," he told reporters. "You could destroy the world 50 times over, 100 times over. And here we are building new nuclear weapons, and they're building nuclear weapons."

For some optimists, the prospects for joint efforts by Trump and Putin to promote nuclear nonproliferation are raising cautious hopes that they could help create an opening to start dialogue in pursuit of a solution to North Korea's nuclear conundrum.

But it remains to be seen whether the leaders can work together on the North Korean issue, considering a raft of tricky challenges ahead for Trump's priority agenda of brokering an end to the protracted war in Ukraine.

"President Trump is talking with the two leaders at the center of this war. An initial ceasefire for a month covering critical infrastructure represents progress -- they have cleared one hurdle," Patrick Cronin, chair for Asia-Pacific Security at the Washington-based Hudson Institute, told Yonhap News Agency via email.

"But there are many more difficult hurdles ahead. The resumption of war in Gaza is a poignant reminder of the fleeting nature of many ceasefires. But I applaud attempts that aim for peace and diplomatic dividends, even if I also caution about making phone peace deals that send the wrong signals to potential aggressors in Asia," he added.

Trump's repeated mention of North Korea as a "nuclear power" and his recent juxtaposition of the North alongside the de facto nuclear powers of India and Pakistan have raised concerns that his immediate focus may not be on the North's nuclear disarmament, despite his stated pursuit of the "complete" denuclearization of the North.

"I don't think Trump is focused on denuclearization anymore ... He is a very pragmatic person," Victor Cha, Korea Chair at the Center for Strategic and International Studies, said during a public event last week.

"Given the size of the (North's nuclear) program, I am sure he thinks there's no way they are going to give up all this stuff."

Even if the United States and Russia move toward nuclear arms control efforts, it remains unclear whether Pyongyang would engage in security talks with Washington at a time when it relies on food, fuel, security assurances and other kinds of support from Moscow.

Along with Russia, the U.S. appears intent to engage in talks on the reduction of China's burgeoning nuclear arsenal.

According to a Pentagon report in December, China is expected to have 1,000 nuclear weapons by 2030, while it is thought to have approximately 600 nuclear warheads in its inventory. China has reportedly rejected U.S. overtures to engage in arms control talks as it has decried the U.S.' arms exports to Taiwan. (Yonhap)