Moscow has repeatedly accused the new authorities in Kiev and the protesters who toppled pro-Moscow president Viktor Yanukovych of being extremists, nationalists and even "Nazis".
Today Putin told senior officials at Russia's FSB security service, the successor to the KGB, that "nationalist and neo-Nazi structures and fighters" in Ukraine had been financed from abroad through non-government organisations (NGOs).
"Russian legislation creates every condition for transparent free activities by NGOs, but we will never let them be used for destructive aims the way it happened in Ukraine," Putin said.
Since returning to the Kremlin for a third term in 2012, Putin has tightened controls over NGOs, signing legislation forcing those with international funding to register themselves as "foreign agents."
In February, seven activists who took part in a rally against Putin's return to the Kremlin were jailed for up to four years and a prominent environmentalist who criticised the impact of the Sochi Olympics was jailed for three years over a protest.