Russia's President Vladimir Putin says he will consider his options if the West fails to meet his demands for security guarantees stopping NATO's expansion to Ukraine.
Moscow earlier this month submitted draft security documents demanding that NATO denies membership to Ukraine and other former Soviet countries and rolls back its military deployments in Central and Eastern Europe.
The Kremlin presented the demands amid tensions over a Russian troop build-up near Ukraine in recent weeks that has fuelled Western fears of a possible invasion.
US President Joe Biden warned Russia's leader in a video call earlier this month that Russia will face "severe consequences" if it attacks Ukraine.
Russia has denied intending to launch an invasion. It also accused Ukraine of planning to try and reclaim control of territories held by Moscow-backed rebels by force – which Ukraine has denied.
Mr Putin has urged the West to move quickly and meet his demands, warning that Moscow will have to take "adequate military-technical measures" if the West continues its "aggressive" course "on the threshold of our home".
When asked what Moscow's response could be, he said, in comments aired by Russian state TV on Sunday, that "it could be diverse", adding that "it will depend on what proposals our military experts submit to me".
The US and allies have refused to offer Russia the kind of guarantee on Ukraine that the Russian President wants, reiterating the NATO principle that membership is open to any eligible country.
They agreed, however, to launch security talks with Russia next month to discuss its concerns.