Priti Patel has defended stringent checks on Ukrainian refugees because they might be Russian agents bringing biological weapons into the UK.
Speaking at Conservative Party Spring Conference in Blackpool, the Home Secretary said it was "naive" to believe women could not be "covert operatives".
And she claimed Vladimir Putin could exploit refugee flows to send agents to Britain.
In her keynote speech, she said: "I've been asked why couldn't we suspend security checks on people escaping Putin's war?
"Times of conflict, my friends, emphasises our need to remain watchful. I know from the briefings I receive from the intelligence and security services that instability around the world brings with it greater threats."
"Only four years ago the Russian military intelligence services used a chemical weapon on British soil."
She went on: "The truth is that a very small number of people can wreak utter havoc. Russia has a history of covert hostile activity.
"And I'm afraid it is naive and misguided to think that only men can be covert operatives, or that refugee flows could not be subject to some form of exploitation."
Ms Patel went on: "There are those who would come to our country, to this country, who mean us harm and who plot to strike at our very way of life.
"The processes that we have put in place closely follow the advice of our intelligence and security services.
"They mean we can help Ukrainians in need without making our country less safe."
It comes as the Home Office said 8,600 visas had been granted under the family scheme for Ukrainians fleeing the war by 5pm on Friday.
Ms Patel added: "State threats and terrorism take many forms. They also thrive on indifference and appeasement and now we are seeing them bolstered by new types of targeted biological, chemical, cyber warfare, ransomware and online threats.
"Our duty is to safeguard our country's interests and we will never take our eye off the ball when it comes to the safety and security of our country."
Education Secretary Nadhim Zahawi said 100,000 places had been created in schools for children fleeing Ukraine and virtual lessons created during the coronavirus pandemic had been translated into Ukrainian.
Levelling Up Secretary Michael Gove confirmed more than 150,000 households had now offered to house Ukrainian refugees, the majority of whom have made their way to Poland.
Former prime minister David Cameron announced on Friday he was driving a "small lorry" to the Polish border with Ukraine with supplies.
