More than two-thirds, 69 percent, of those who responded to a CNN poll said they believe Russia is a threat to the United States. That puts Russia close to North Korea and Iran, viewed as threats by about 70 percent of the public.
"That's a 25-percentage point increase since 2012 and represents the highest number on that question since the break-up of the Soviet Union," Keating Holland, CNN's polling director, said.
At the same time, 68 percent of respondents said they have a negative view of Putin, while only 11 percent have a positive one. Holland said Putin's standing has fallen 14 percentage points in a month.
Crimea, in a move backed by Russia, is scheduled to vote Sunday on seceding from Ukraine, and Russia is staging military exercises near the border involving thousands of soldiers.
About 70 percent of those polled said Russia's response to the change of government in Ukraine is unjustified and 80 percent said Russian actions violate international law.
The polling company ORC interviewed 801 people between last Friday and Sunday. The margin of error is 3.5 points.