Russia was ready to bring its nuclear weapons into a state of alert during last year's tensions over the Crimean Peninsula and the overthrow of Ukraine's president, President Vladimir Putin said.
Mr Putin also expanded on a previous admission that the well-armed forces in unmarked uniforms who took control of Ukrainian military facilities in Crimea were Russian soldiers.
Mr Putin's comments, in a documentary being shown on state TV, highlight the extent to which alarm spread in Russia in the weeks following Ukrainian president Viktor Yanukovych's ousting in February 2014 after months of street protests that turned increasingly violent.
The documentary comes as speculation swirls about Mr Putin's 10-day absence from public view. Tomorrow, he will meet with the president of Kyrgyzstan in an event covered by the news media, which would be his first appearance before journalists since March 5.
After Mr Yanukovych fled Kiev, eventually surfacing in Russia, separatist sentiment soared in Crimea, the Black Sea peninsula dominated by ethnic Russians.
Russian forces took control of Ukrainian military facilities on the peninsula and a referendum on secession was hastily called. The referendum, which was widely denounced in the West as illegitimate, reportedly brought overwhelming support for secession. Russia annexed Crimea on March 19, 2014.
In the documentary, which marks a year since the referendum, Mr Putin said of the nuclear preparedness: "We were ready to do this ... (Crimea) is our historical territory. Russian people live there. They were in danger. We cannot abandon them."
The comments were reported on the state broadcaster's website after its transmission in the Russian Far East and before it appeared on the air in Moscow.
Mr Putin said his plans for a Crimean operation started after Mr Yanukovych fled.
"We never thought about severing Crimea from Ukraine until the moment that these events began, the government overthrow," he said, repeating Russia's contention that Mr Yanukovych was the victim of a coup.
He said he called for a "closed opinion poll" of sentiments among Crimeans about whether to remain in Ukraine.
He did not give details as to how this survey was conducted, but said "it became clear that 75% of the general population desired to join Russia".
Russia initially denied that the unmarked forces who took control in Crimea were Russian, but Mr Putin later admitted they were. In the documentary, he said he ordered the defence ministry to deploy military intelligence special forces, marines and paratroopers "under the cover of strengthening the protection of our military facilities".
Russia's Black Sea Fleet is based in Crimea; it retained the bases after the collapse of the Soviet Union under an agreement with Ukraine.
Mr Putin claimed in the documentary that the number of Russian forces in Crimea never exceeded the 20,000 authorised under the agreement on basing the Black Sea Fleet there.
Mr Putin also said Russian forces helped Mr Yanukovych escape to Russia.
After fleeing the capital Kiev, Mr Yanukovych made one appearance in Kharkov, then disappeared for several days. Reports at the time said he and his security entourage went on a desperate journey through the eastern parts of the country and down to Crimea, looking for safety. Mr Putin's retelling appeared to confirm those reports.
He said Russian security forces had tried to keep contact with Mr Yanukovych as he moved through Ukraine and eventually "we brought him to Russian territory".