The United States said it has called for an open meeting of the UN Security Council next Monday to address the crisis around Ukraine due to what it called "threatening behavior" by Russia.
"More than 100,000 Russian troops are deployed on the Ukrainian border and Russia is engaging in other destabilizing acts aimed at Ukraine, posing a clear threat to international peace and security and the UN Charter," Washington's United Nations envoy Linda Thomas-Greenfield said Thursday in a statement.
"As we continue our relentless pursuit of diplomacy to de-escalate tensions," she added, the 15-member Security Council "must squarely examine the facts and consider what is at stake for Ukraine, for Russia, for Europe, and for the core obligations and principles of the international order should Russia further invade Ukraine."
With fears rising that Russia could invade its neighbour, a former Soviet state, Thomas-Greenfield said the council faced a "crucial" matter for international peace and security: "Russia's threatening behavior against Ukraine and the build-up of Russian troops on Ukraine's borders and in Belarus."
She added: "This is not a moment to wait and see. The Council's full attention is needed now, and we look forward to direct and purposeful discussion on Monday."
As one of the five permanent members of the Security Council, Russia has veto power over any United Nations resolution brought to the council.
But Thomas-Greenfield said the meeting will be more of an opportunity to "expose Russia" for its actions and isolate the Kremlin for its aggressive posture regarding Ukraine.
"And while they do have the veto power, their isolation will be felt if the Security Council brings this, and we present a united front against the Russians," the American envoy said in an interview on Romanian Public Television.
"I don't think any country in the Security Council will sit back and say it's OK for Russia to invade the borders of another country."
Originally the United States had hoped to hold the Security Council meeting on Friday, according to diplomats.
But they said they agreed to push it to Monday so as not to interfere with a scheduled Friday phone call between French President Emmanuel Macron and his Russian counterpart Vladimir Putin.