Gavin Williamson said if there was ever any doubt over the threat posed by Moscow “we only have to look at events in Salisbury, where our Armed Forces, including the RAF, have been responding to a cold-blooded chemical attack”.
Theresa May has said it is “highly likely” Russia was involved in the attack which targeted former spy Sergei Skripal and his daughter Yulia with Russian-made nerve agent group novichok.
Moscow has denied any involvement in the case, which has caused a standoff between Britain and Russia.
Mr Williamson said the Kremlin’s response has been to “unleash a tidal wave of smears, lies and mockery”.
The Defence Secretary, writing in the Sunday Telegraph to mark 100 years since the formation of the Royal Air Force, highlighted the conflicts in countries such as Yemen, Syria and North Korea, saying the world was becoming a “darker, more dangerous place”.
“Then there is President Putin,” he said.
“He is using more hybrid capabilities to subvert, undermine, and influence countries around the world. We have entered a new era of warfare”.
He added: “It’s vital for UK defence to keep evolving to meet the threats of tomorrow to keep our country safe and protect the hard-earned freedoms and way of life we enjoy today.”
Mr Williamson called the attack on British soil “illegal and contemptuous”, saying it endangered innocent lives.
He had previously told Russia it should “go away and shut up”.
The poisoning on 4 March sparked a global diplomatic spat. More than 100 Russian diplomats have been expelled by Western countries, including 23 from Britain.
Russia had already retaliated in kind by ejecting 23 British diplomats, and the Russian embassy in London published a list of 14 questions over the case.
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Mr Skripal and his daughter were found slumped on a bench after being poisoned.
Shop owners in Salisbury have said they are struggling in the wake of the attack which happened a month ago, with business down 90%.