Andrew Parker has accused the Kremlin of "flagrant breaches of international rules"
The head of Britain’s domestic counter-intelligence agency has accused the Russian government of “bare-faced lying" and "criminal thuggery."
The director general of MI5 Andrew Parker launched the blistering attack on Vladimir Putin's regime during a speech to European intelligence agencies in Berlin.
He said the Kremlin was using its spies and military to carry out "flagrant breaches of international rules."
"Bare-faced lying seems to be the default mode, coupled with ridicule of critics," he said.
"The Russian state's now well-practised doctrine of blending media manipulation, social media disinformation and distortion, along with new and old forms of espionage and high-levels of cyber attacks, military force and criminal thuggery is what is meant these days by the term 'hybrid threats'."
Mr Parker said the Russian government was the "chief protagonist" trying to undermine European democracies with "malign activities" adding that the country risked becoming a more "isolated pariah."
The UK believes it is highly likely that the Russian State orchestrated the nerve attack on former double agent Sergei Skripal and his daughter in Salisbury in early March.
The Kremlin has denied any involvement.
Britain’s chemical weapons research facility has admitted that, while it can confirm novichok was the substance used, it cannot tell where it was manufactured.
Novichok is a military-grade nerve agent developed by Russia from the 1970s onward - however the country’s president Vladimir Putin has warned that it could be produced in up to 20 countries.
Mr Parker also said 12 terror plots have been thwarted in the UK since March last year, taking the total number of disrupted attacks in the UK to 25 since 2013.
And in a nod to Brexit, he said co-operation with EU partners was essential to guard against the threats from Islamist militants and Russia.
"We must not risk the loss of mutual capability or weakening of collective effort across Europe," Mr Parker said.
"We owe that to all our citizens across Europe."
Mr Parker accused the Russian State of carrying out a nerve agent attack in Salisbury, supporting the Syrian government despite its use of chemical weapons on civilians, invading Crimea, seeking to interfere in elections in the US and France, attempting to mount a coup in Montenegro and carrying out cyber attacks on Western institutions.