The Biden administration announced on Tuesday that it was working with gas and crude oil suppliers from West Asia, North Africa and Asia to bolster supplies to Europe in the coming weeks, in an effort to blunt the threat that Russia could cut off fuel shipments in the escalating conflict over Ukraine.

European allies have been cautious in public about how far they would go in placing severe sanctions on Moscow if it invades Ukraine. Germany has been especially wary; it has shuttered many of its nuclear plants, increasing its dependence on natural gas imports to generate electricity.

Many European officials have said they suspect President Putin instigated the current crisis in the depths of winter for a reason, calculating that he has more leverage if he can threaten to turn off Russian fuel sales to Europe.

So in recent weeks, American officials have been planning an effort that has echoes of the Berlin airlift, the attempt to keep West Berlin supplied in the face of a Soviet blockade in 1948 and 1949. That event led to the creation of Nato, the defensive alliance that Putin is hoping to undercut by massing troops along the Ukrainian border.