G-7 countries on Wednesday asked Russia to stop the referendum process under way in Crimea, saying they will not recognise its outcome. If Russia annexed Crimea, "we will take further action, individually and collectively", the countries said in a joint statement.
The referendum has been called by Moscow’s Crimean supporters to determine if the territory should remain with Ukraine or opt to join Russia.
Crimea’s Parliament on Tuesday passed a motion stating that it would become independent in the event of a yes vote and then seek to join the Russian Federation.
But the G-7 countries — the US, UK, Japan, Germany, France, Canada, Italy and the European — said "such a referendum would have no legal effect".
"Given the lack of adequate preparation and the intimidating presence of Russian troops, it would also be a deeply flawed process which would have no moral force. For all these reasons, we would not recognise the outcome."
But, if the Russian federation were to go ahead and annexed Crimea, the group warned, "we will take further action, individually and collectively".
Together, as a group, the seven countries have already suspended preparatory meetings for the G-8 summit Russia is hosting in Sochi in June.
They have done more separately.
The United States, for instance, has slapped visa restriction on Russians and Ukrainians responsible for the unrest in Crimea and in the rest of Ukraine.
And it has also put in place targeted sanctions against individuals and entities responsible for violating the territorial integrity of Ukraine.
President Barack Obama is receiving Ukrainian Prime Minister Arseniy Yatsenyuk for a bilateral meeting sat the White House later on Wednesday.