UNITED NATIONS — U.S. Secretary of State Rex Tillerson appealed to the international community, especially Russia and China, to stop the spread of nuclear weapons, calling North Korea a case study of the failure to prevent rogue states from obtaining weapons of mass destruction.

U.S.-Russian relations are at a low point, but Tillerson recalled the cooperation between Washington and Moscow during the Soviet era, despite their Cold War rivalry, on measures to stop the threat of nuclear weapons proliferation. And he said “we should do so again.”

“We especially ask Russia to examine how it can better support global nonproliferation efforts,” Tillerson said. “If Russia wants to restore its role as a credible actor in resolving the situation with North Korea it can prove its good intentions by upholding its commitments to establish international efforts on nuclear security and arms control.”

As for China, he said Beijing’s cooperation is essential to prevent “a catastrophe” and conflict on the Korean Peninsula. If China truly wants to denuclearize the peninsula, he said it should work “to put the kind of pressure on North Korea that can change its strategic calculation before it’s too late.”

Tillerson said North Korea “is a case study in why nations must work to preserve and strengthen global nonproliferation norms.”

North Korea joined the Nuclear Nonproliferation Treaty in the mid-1980s but it “cheated” and was never held accountable, he said. It withdrew from the treaty in 2003 and carried out its first underground nuclear test in 2006.

Tillerson said there were also lessons for Iran “which was on its own path to develop nuclear weapons” and “seems keen to preserve for itself the option to resume such work in the future,” allegations strongly denied by Iran’s President Hassan Rouhani.

Tillerson spoke Thursday at a ministerial meeting of the U.N. Security Council called by the United States on “the acute threat” posed by the proliferation of nuclear, chemical and biological weapons. It cited three countries in a note to council members that have been targeted by council resolutions — North Korea, Iran and Syria.

Russia’s U.N. Ambassador Vassily Nebenzia took issue with the meeting, saying a discussion on nonproliferation “should be general, not pegged to someone’s idea of ‘pariah states.'” He said a U.S. “concept note” sent to council members before the meeting “artificially links three country situations which have absolutely nothing to do with each other.”

He said “further prospects in the field of nonproliferation cannot be considered in isolation from the overall security” situation. This means taking into account all factors that affect security — “first and foremost” the U.S. deployment of the Terminal High-Altitude Area Defense System, also known as THAAD, and “NATO’s joint nuclear mission.”

Tillerson said the U.S. never mentioned “a trigger for accelerated development by some states of weapons of mass destruction” — the toppling of Iraqi leader Saddam Hussein whose country was invaded in the mistaken belief that he had nuclear weapons and the overthrow of Libyan leader Moammar Gadhafi who voluntarily renounced the development of nuclear weapons

“This doesn’t in any way, of course, justify the DPRK’s missile and nuclear program, but to ignore the reasons for them is to be very short-sighted,” Nebenzia said, using the initials of North Korea’s official name, the Democratic People’s Republic of Korea.

During the council meeting, speaker after speaker including U.S. allies in Europe and Japan spoke out in support of the 2015 nuclear deal that capped Iran’s nuclear program, which President Donald Trump is threatening to scrap.

Nebenzia expressed hope that “common sense will prevail in the end” and “the irresponsible” attempt to torpedo the agreement, known as the JCPOA, will be stopped.

The Russian ambassador then said he had to correct his early statement about North Korea, Iran and Syria not being linked.

“Iran and the DPRK today do find themselves linked — because if the United States does leave the JCPOA, this will be the worst signal we can send to North Korea, Nebenzia said.

“In fact more intensive diplomatic efforts are now needed in the Korean Peninsula and one needs to start now without wasting any timel,” he said.

Russia and China again urged adoption of their freeze-for-freeze proposal that would halt North Korean nuclear and missile tests in exchange for the U.S. and South Korea stopping their joint military exercises. But the Trump administration has rejected it.

China’s Foreign Minister Wang Yi told the council it is “a practical way out” and stressed that China had “made tireless efforts for settlement to the North Korean issue.”

He said sanctions are important “to promote a resumption of talks and dialogue” in North Korea. He added that “it is necessary to exercise pressure, as appropriate, if countries blatantly violate” agreements and Security Council resolutions.

“But sanctions are not the panacea,” Wang said. “Dialogue and negotiations present the fundamental way out.”