Ukraine crisis: Biden warns Russia may invade next month

US President Joe Biden has warned there is a "distinct possibility" Russia might invade Ukraine next month, the White House says.

Russia meanwhile says it sees "little ground for optimism" in resolving the crisis after the US rejected Russia's main demands.

The build-up of tens of thousands of Russian troops on Ukraine's borders in recent weeks has stoked fears of an invasion.

Russia denies it is planning an attack.