The US has given Russia its written responses to a set of security demands by Moscow over Ukraine and NATO amid fears President Putin’s troops could invade the country.
US Secretary of State Antony Blinken said the “ball is in Russia’s court”, as he added: “We’re ready either way.”
Russia has massed about 100,000 troops near the Ukrainian border in recent weeks and is holding military drills at multiple locations in Russia and neighbouring Belarus, which also borders Ukraine.
Moscow has denied it is planning an assault on the nation.
Mr Blinken said the US response made no concessions to Moscow’s main demand that Ukraine be prevented from ever joining NATO.
He said the document, handed to officials in the Russian capital, outlines a diplomatic path forward if the Kremlin takes it seriously, as America tries to avert an military offensive.
It contains a “principled and pragmatic” evaluation of Moscow’s concerns and reflects that the US is open to dialogue and prefers diplomacy.
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He also said Ukraine and Washington’s European allies were closely involved in drawing up the document which he said would not be made public.
Some 8,500 US troops have been put on heightened alert to go to eastern Europe to bolster NATO forces.
Among the other demands, Moscow wants NATO to curtail other actions, including stationing troops in former Soviet bloc countries.
NATO secretary-general Jens Stoltenberg has called on Russia to immediately de-escalate the situation.
He told reporters: “NATO firmly believes that tensions and disagreements must be resolved through dialogue and diplomacy.”
He also repeated his call for Moscow and the pact to re-establish their respective offices in Brussels and Moscow, and to use military communication channels to promote transparency and reduce risks.
Earlier, the Kremlin warned it would quickly take “retaliatory measures” if the US and its allies reject its security demands and continue their “aggressive” policies.