Putin refused to rule out invading Ukraine, suggesting the US has been trying to destroy Russia since 1918

• Vladimir Putin refused to rule out a Russian invasion of Ukraine.
• Putin slammed NATO expansion and said Russia was defending itself from the bloc's aggression.

President Vladimir Putin refused to rule out a Russian invasion of Ukraine, claiming the US and the West had been trying to break up Russia since 1918.

Speaking during the Q&A section of his annual speech, which took place Thursday, Putin said NATO was putting "constant pressure" on Russia by expanding eastward toward it.

Russia has been building up its troop presence on its border with Ukraine, prompting fears of an imminent invasion.

When asked by Sky News' Diana Magnay if he would rule out invading Ukraine, Putin said his country would do what it needed to protect itself.

"Our actions will depend not on the negotiation process but on the unconditional security of Russia," he said.

"We've witnessed five waves of NATO expansion. Why can't they understand? What is unclear? We are thinking about our own security."

Putin also said troop buildup at Ukraine's border was a direct response to US aggression, citing the placement of US missile systems in Ukraine.

"The US is deploying its missiles close to our home, on the porch of our house," Putin said. "What would the Americans think if we came to the border between Canada or the US, or Mexico, and deploy our own missiles over there?"

The US has not deployed advanced missiles to Ukraine capable of striking Russia, but has consistently offered Kiev support amid ongoing tensions with Moscow.

Since 2014, the US has provided Ukraine with over $2.5 billion worth of security assistance, including Javelin anti-tank missiles. That year, Russia invaded and annexed Crimea from Ukraine.

The Kremlin has since 2014 also backed separatists in a war against Ukrainian troops in the eastern Donbass region, and the conflict has claimed over 13,000 lives.

Experts say that Putin views Ukraine — a former Soviet republic — as unfinished business, and warn that he's looking for an excuse to invade and blame it on the US and NATO.

President Joe Biden has warned of severe economic consequences against Russia if it invaded Ukraine, but recently said the US was not obligated to deploy troops in the event of a Russian military incursion.

Magnay on Thursday also asked Putin what the West "does not understand about Russia," to which Putin suggested that the US had been trying to break up Russia for more than 100 years.

"Here's the thing. Back in 1918, one of the assistants of Woodrow Wilson, the US president, said that the whole world would feel calmer and safer if today's enormous Russia would be replaced with the states of Siberia and four more states in the European part of Russia," Putin, a former KGB operative, said.

"In 1991 we separated in 12 separate parts," Putin said. "It seems to be our partners aren't satisfied with that, they think that Russia is too large."