At a meeting intended to be a face-to-face confrontation between top diplomats from the United States, Russia and Ukraine, Secretary of State Antony Blinken delivered a tough message to Russia and world powers that "reckless nuclear threats must stop immediately."

His remarks echoed the speech President Biden delivered to the U.N. on Wednesday, in which Mr. Biden accused Russian President Vladimir Putin of "making irresponsible threats to use nuclear weapons." Just hours earlier, Putin ordered the partial mobilization of hundreds of thousands of additional Russian troops and suggested the possible use of nuclear weapons.

In his Thursday speech, Blinken also quoted Ukrainian President Volodymyr Zelenskyy, whose pre-recorded remarks were played in the General Assembly Hall on Wednesday, saying "diplomacy is the only way to end this war."

"Diplomacy cannot and must not be used as a cudgel to impose on Ukraine a settlement that cuts against the U.N. charter, or rewards Russia for violating it," Blinken added.

He then laid out what he called Russia's "diabolical strategy" of uprooting Ukrainians and relocating Russian citizens to Russian-occupied land; holding a "sham referenda"; annexing the territory; and then defending the areas that it would consider its own territory.

"One man chose this war. One man can end it," Blinken said, referencing Putin. "Because if Russia stops fighting, the war ends. If Ukraine stops fighting, Ukraine ends."

Blinken's speech was given to the 15-nation Security Council during the United Nations General Assembly. However, Russia's Foreign Minister Sergey Lavrov was not in the chamber for Blinken's remarks. He arrived to deliver his own speech and left promptly after.

In his speech, Lavrov blamed Western nations — citing the U.S., France, and Germany — for imposing "a completely different narrative about Russian aggression" and referred to alleged violations of rights by "mercenaries" "who are citizens of the U.K., Canada, the U.S. and the Netherlands." He also cited unspecified "threats against Russian security."

The result was clear to most nations calling for diplomatic efforts — that a diplomatic solution to Russia's war against Ukraine would not materialize during the meeting.

France, as President of the Council for September, had called the meeting. French Foreign Minister Catherine Colonna accused Russia of "unspeakable crimes" and called for accountability. International Criminal Court (ICC) prosecutor Karim Khan told the council that the ICC is sending investigators to Ukraine to look into allegations of war crimes and crimes against humanity, after opening an investigation six months ago.

When it came time for Ukrainian Foreign Minister Dmytro Kuleba to speak Thursday, he said that "there will be no peace without justice," and repeated his president's call for the establishment of a special tribunal.

Rafael Grossi, director-general of the International Atomic Energy Agency, told reporters at the U.N. on Wednesday that the largest nuclear power plant in Europe, Ukraine's Zaporizhzhia, was shelled this week, saying, "We are playing with fire."

At the council meeting on Thursday, Chinese Foreign Minister Wang Yi supported the call for investigations into violations of international law, urging restraint. China's foreign minister had not planned to attend the U.N. high-level session, the mission told CBS News. But he will now meet with Blinken on Friday, the State Department announced, to discuss "a range of bilateral and global issues."

China's leader, Xi Jinping, acknowledged unspecified "concerns" about the fighting in Ukraine in mid-September.

U.N. Secretary General António Guterres, who was responsible for brokering a grain deal between Ukraine and Russia in July, was skeptical of a peace deal.

"Russia's war in Ukraine shows no sign of letting up," he said, adding that the seven months of war "have seen unspeakable suffering and devastation."

Lavrov is expected to speak to the General Assembly on Friday.