Izumi Nakamitsu didn't name any countries but she was clearly referring to the United States and Russia, and possibly China, when she told the UN Security Council that "relationships between states - especially nuclear-weapon states - are fractured." "So-called great power competition is the order of the day," Nakamitsu said

United Nations: The UN disarmament chief warned Wednesday that the spectre of an unbridled nuclear arms race is threatening the world for the first time since the 1970s, the height of the Cold War between the United States and the former Soviet Union. Izumi Nakamitsu didn't name any countries but she was clearly referring to the United States and Russia, and possibly China, when she told the UN Security Council that "relationships between states - especially nuclear-weapon states - are fractured."

"So-called great power competition is the order of the day," Nakamitsu said.

"Division, distrust and a dearth of dialogue are increasingly the norm." Russia-US relations have been at post-Cold War lows since Moscow's 2014 annexation of Ukraine's Crimea.

Last year, Russia and the US both withdrew from the 1987 Intermediate-range Nuclear Forces Treaty, the US saying it pulled out because of Russian violations and the Kremlin denying breaching the treaty's terms.

Russia has said the US also appears reluctant to extend the New START treaty, the only treaty governing the number of strategic nuclear weapons deployed by the two countries, which expires in 2021.

Last week, US Défense Secretary Mark Esper touted a multibillion-dollar plan for a top-to-bottom modernization of America's nuclear arsenal to keep up with Russia and outpace China.

In late December, Russia's defence minister reported to President Vladimir Putin that a new intercontinental weapon that can fly 27 times the speed of sound had become operational, bolstering the country's nuclear strike capability.

Nakamitsu warned that "the spectre of unconstrained nuclear competition looms over us for the first time since the 1970s."

"We are witnessing what has been termed a qualitative nuclear arms race - one not based on numbers but on faster, stealthier and more accurate weapons," she said.

"Regional conflicts with a nuclear dimension are worsening, and proliferation challenges are not receding."

The Security Council meeting was requested by Germany to commemorate the 50th anniversary of the Nuclear Non-Proliferation Treaty on March 5 and to support the upcoming conference to review and advance its goals which starts April 27 and ends May 22.

Russia and the United States clashed at the meeting over the breakdown in arms control negotiations.

But they supported a statement by the 15-member Security Council saying the treaty, known as the NPT, "remains the cornerstone of the nuclear non-proliferation regime and the foundation for the pursuit of nuclear disarmament and the peaceful uses of nuclear energy."

The council resolved to advance the NPT's goals and underlined the treaty's essential role "in the preservation of international peace, security and stability as well as the ultimate objective of a world without nuclear weapons."

Germany's Foreign Minister Heiko Maas told the council that despite its achievements "the NPT is facing serious setbacks: Nuclear disarmament has come to a standstill. New technologies are creating dangerous strategic imbalances. And proliferation crises are demanding our fullest attention."

He pointed to North Korea acquiring nuclear weapons, disregarding the NPT and Security Council resolutions, as a key failure.

Maas said the only realistic way ahead is applying pressure and stepping up nuclear diplomacy.

He urged international support for US efforts to negotiate with North Korea, and for the 2015 Iran nuclear deal which "remains the best and only promising tool to keep Iran from obtaining nuclear weapons."