Speaking in Uzbekistan, Putin's comments came in response to calls within some NATO member states to allow Ukraine to hit targets inside Russia.

"This constant escalation can lead to serious consequences," Putin said.

"In Europe, especially in small countries, they should be aware of what they are playing with," he added.

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The Russian leader said leaders should bear in mind the "small territory" and "dense population" of many European countries.

"And this factor, which they should keep in mind before they talk about striking deep into Russian territory, is a serious thing."

He said that while Ukraine would carry out the strikes, the responsibility for them would lie with Western suppliers of the weapons.

"They want a global conflict," he added.

Putin also said that while he believed Western military instructors were already in Ukraine operating undercover as mercenaries, countries such as France sending them officially would be another "escalation."

"It is another step towards a serious conflict in Europe, towards a global conflict," he said.

Ukraine's top commander announced Monday that talks were being held with France on sending military instructors to the country.

"There are specialists there under the guise of mercenaries," Putin said, adding that "this was nothing new."

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He said that they would be "defeated" by the Russian army and that "we will do what we think is necessary regardless of who is on the territory of Ukraine."

"They should be aware of this," Putin said.