UNITED NATIONS -- UN Secretary-General Antonio Guterres warned Wednesday that an escalation of the conflict in Ukraine is "a clear and present danger."

"Over the past year, not only have we seen suffering and devastation grow, it is also becoming more evident just how much worse it could all still become. The possible consequences of a spiraling conflict are a clear and present danger," he told a resumed emergency special session of the UN General Assembly.

The conflict in Ukraine is also fanning regional instability and fueling global tensions and divisions, while diverting attention and resources from other crises and pressing global issues, he said.

"Meanwhile, we have heard implicit threats to use nuclear weapons. The so-called tactical use of nuclear weapons is utterly unacceptable. It is high time to step back from the brink," he said.

Guterres called for peace.

People in Ukraine are suffering enormously. Ukrainians, Russians and people far beyond need peace, he said. "While prospects may look bleak today, we must all work, knowing that genuine, lasting peace must be based on the UN Charter and international law."

The longer the fighting continues, the more difficult this work will be, he warned. "We don't have a moment to lose."

The 11th emergency special session of the General Assembly resumed on Wednesday as the conflict between Russia and Ukraine is approaching its first anniversary.