Moscow (AFP) - President Vladimir Putin has revealed the moment he says he gave the secret order for Russia's annexation of Crimea and described how Russian troops were ready to fight to rescue Ukraine's deposed, pro-Moscow president.

In a trailer shown Sunday for an upcoming documentary on state-run Rossiya-1 television called "Homeward bound", Putin openly discusses Moscow's controversial grabbing of Crimea a year ago.

Putin recounts an all-night meeting with security services chiefs to discuss how to extricate deposed president Viktor Yanukovych, who had fled a pro-Western street revolt in the Ukrainian capital Kiev.

"We ended at about seven in the morning," Putin says. "When we were parting, I said to my colleagues: we must start working on returning Crimea to Russia."

Four days after that February 2014 meeting, unidentified soldiers took over the local parliament in Crimea and deputies hurriedly voted in a new government. The Ukrainian province was then formally annexed by Moscow on March 18, triggering international condemnation.

The military operation was initially kept secret and despite the increasingly obvious actions of unmarked Russian forces on the ground, Moscow insisted that only locals were involved in the upheaval. Later, the Kremlin conceded that it had been behind the power grab.

In the trailer for the documentary, Putin also claims that Russia's military was ready to fight its way into the eastern Ukrainian city of Donetsk to get Yanukovych, a heavily corrupted but loyal figure who favoured keeping Ukraine in Russia's sphere of influence.

"He would have been killed," Putin said. "We got ready to get him right out of Donetsk by land, by sea or by air," he said. "Heavy machineguns were mounted there to avoid talking too much."

Yanukovych later resurfaced in the southern Russian city of Rostov and has not been back to Ukraine.

More than 6,000 people have since been killed in fighting between Ukraine's government forces and heavily armed separatist militias based in Donetsk and backed -- according to Western governments -- by Russia, although Moscow denies this.

Rossiya-1 did not say when the full documentary would be aired.