President Vladimir Putin says Russia quietly conducted an opinion survey to gauge Crimeans' appetite for annexation shortly before the March 2014 referendum on the issue.

Putin made the comments in an excerpt from a documentary film that state-run Rossia-1 television says will air soon.

"You understand, a closed survey was conducted," Putin said in the footage broadcast on March 9.

He said it showed 75 percent of Crimean residents wanted to join Russia, and added "it became clear to me that if we came to this, the number of people who would want this historic event to happen would be much higher."

According to the official results of the March 16 referendum, denounced by Kyiv and the West as illegitimate, about 97 percent of voters supported joining Russia.

Gunmen were in evidence at polling stations and the atmosphere of intimidation was thick at the time.

Excerpts from the film have added to evidence that Russia's takeover of Crimea from Ukraine was carefully planned operation rather than a response to the will of citizens on the peninsula.

In a trailer broadcast on March 8, Putin said he told senior security officials on February 23, 2014, that "we will have to start work to return Crimea to Russia."