MOSCOW — Russia would have activated its nuclear arsenal if necessary a year ago when its troops secured the Crimean peninsula and carried out a referendum on the strategic peninsula’s secession from Ukraine, Russian President Vladimir Putin said in a documentary that aired Sunday.

In the report timed to Monday’s anniversary of the referendum, “Crimea: Path to the Motherland,” Putin justifies Moscow’s seizure of the Black Sea territory as necessary to protect Russians and military bases from what he described as a nationalist junta that had taken power in Kiev.

Putin accused the United States of masterminding the three-month uprising in the Ukrainian capital that ended with the ouster of Kremlin-allied President Viktor Yanukovich, who has since taken refuge in Russia.

The documentary presented a vibrant and defiant image of the Russian president, who hasn’t been seen in public for more than a week, spurring rumors that he is sick or has been deposed in a palace coup.

The documentary covered the year since the March 16 referendum in which 97 percent of voters among Crimea’s 2 million residents were said to have supported secession. Two days later, Putin issued a decree annexing the peninsula, which is home to Russia’s Black Sea fleet and Soviet-era air bases.

Part of the operation to secure Crimea from the unrest that has spread across eastern Ukraine since Yanukovich was deposed on Feb. 21, 2014, included the deployment of K-300P Bastion coastal defense missiles to demonstrate Russia’s willingness to protect the peninsula from military attack, Putin said in one excerpt of the documentary that aired Sunday night on Rossiya-1 television.

“We deployed them in a way that made them seen clearly from space,” Putin said of the missiles.

He also said the Russian military had been prepared to put nuclear weapons on alert if necessary.

Putin said he ordered the Crimean operation to protect the Russian community there.

“We cannot let the people be pushed under the steamroller of the nationalists,” he said of the decision made immediately after Yanukovich fled Kiev.

“Our goal was not to take Crimea by annexing it. Our final goal was to allow the people to express their wishes on how they want to live,” Putin said.

Crimea was conquered by czarist Russia in the late 18th century and remained part of the Russian Federation after the Bolshevik Revolution of 1917. But in 1954, Ukrainian-born Soviet leader Nikita S. Khrushchev ceded the peninsula to the Ukrainian Soviet Socialist Republic. At the time, the gesture had little strategic significance, because the two republics had common armed forces and were within the same country.

Crimea became part of independent Ukraine in the 1991 breakup of the Soviet Union, a fact that has grated on Russian nationalists ever since.