The number of nuclear weapons held by world powers declined in the past year, but future reductions look uncertain because of the "political and military differences" between Moscow and Washington, an influential research group says.
The Stockholm International Peace Research Institute (SIPRI), in its annual report issued on June 17, said that at the start of 2019, Russia, the United States, and seven other countries possessed 13,865 nuclear weapons.
That's a "marked decline" from the 14,465 estimated at the start of 2018, SIPRI said.
The decrease "is due mainly to Russia and the U.S. -- which together still account for over 90 percent of all nuclear weapons -- further reducing their strategic nuclear forces" through implementation of the so-called New START treaty, while also making unilateral reductions.
However, it said, New START will expire in 2021 unless both parties agree to extend it.
"There are currently no discussions about extending New START or negotiating a follow-on treaty," said Shannon Kile, director of SIPRI’s Nuclear Disarmament, Arms Control, and Nonproliferation Program.
"The prospects for a continuing negotiated reduction of Russian and U.S. nuclear forces appears increasingly unlikely given the political and military differences between the two countries," he added.
Andrea Thompson, the U.S. undersecretary of state for arms control, told a Senate panel in May that the "administration has not made any decision on a potential extension of New START."
Russian President Vladimir Putin on June 6 told a meeting with the heads of international news agencies in St. Petersburg that Washington was reluctant to begin talks on extending the deal.
"We do not have to extend it. Our systems can guarantee Russia's security for quite a long period of time," Putin said. "If no one feels like extending the New START agreement, well, we won't do it then."
The pact, signed in Prague in 2010, provided for limiting to 1,550 the number of strategic nuclear warheads deployed by either country -- down almost two-thirds from the 6,000-warhead limit in the original START I treaty, which entered into force in 1994 and expired in 2009.
Moscow and Washington are also at odds over the bilateral 1987 Intermediate-Range Nuclear Forces (INF) Treaty, which eliminated an entire class of missiles.
In February, the United States suspended its participation in the agreement, with Washington and its allies accusing Russia of deploying a missile system that violates the pact.
Russia, which denies the accusation, later followed suit. Moscow accuses the United States of breaking the accord itself, an allegation rejected by Washington.
In its report, SIPRI noted that Russia and the United States were continuing on their "extensive and expensive" efforts to replace and modernize their nuclear warheads, missile- and aircraft-delivery systems, and nuclear-weapon-production facilities.
In 2018, the United States set out plans to develop new nuclear weapons and modify others to allow for expanded military roles and missions.
Along with the United States and Russia, SIPIRI listed Britain, France, China, India, Pakistan, Israel, and North Korea as possessing nuclear weapons.
"China, India, and Pakistan are increasing the size of their nuclear arsenals. India and Pakistan are expanding their military fissile-material-production capabilities on a scale that may lead to significant increases," it said.
The report added that North Korea continued to prioritize its military nuclear program "as a central element of its national security strategy."
U.S. President Donald Trump and North Korean leader Kim Jong Un have twice met in summits designed to forge an agreement over Pyongyang's nuclear program, but little progress has been made.
SIPRI said that of the 13,865 nuclear weapons held by the nine countries, 3,750 are deployed with operational forces, with some 2,000 of them kept in a state of high operational alert, SIPRI said.
But it said that the availability of reliable information on the status of the nuclear arsenals and capabilities of the nuclear-armed states "varies considerably."
"The U.S. and the U.K. have disclosed important information about their stockpile and nuclear capabilities, and France has also declared some information," the research group said.
SIPRI added that Russia "does not make publicly available a detailed breakdown of its forces counted under New START, even though it shares this information with the U.S.A."
It said the Indian and Pakistani governments "make statements about some of their missile tests but provide little information about the status or size of their arsenals."
It added that North Korea and Israel provide little, if any information, about their nuclear weapons.