He said NATO defence ministers meeting in Brussels would discuss plans to counter a "Russian campaign of hostile activities against NATO allies".

"We have seen several examples of sabotage, of arson, attempts of cyber attacks, of disinformation," Stoltenberg said.

He said ministers would work on "response options", expected to include closer intelligence sharing, bolstering protection of critical infrastructure, and "tighter restrictions on Russian intelligence personnel across the alliance".

Western governments have sounded the alarm about what say is a growing wave of Russian hybrid action on NATO territory in Europe.

Poland last month said it would restrict the movements of Russian diplomats after the arrest of several people suspected of planning sabotage attacks on behalf of Moscow's security services.

Authorities in the Czech Republic, Estonia, Germany, Latvia, Lithuania and Britain have also recently investigated and charged people over alleged "hostile" activities blamed on Russia.

Officials suggest Moscow's aim could be to sow discord among NATO allies and to try to pressure them into halting weapons supplies to Ukraine.

"Russia's actions will not stop us from supporting Ukraine," Stoltenberg pledged on Wednesday.