The scale of the terrorism threat to the UK is "unprecedented", the new head of MI6 has said.
Alex Younger said UK intelligence and security services had disrupted 12 terrorist plots since June 2013.
He said many of the threats came from ungoverned spaces in the Middle East - namely Iraq and Syria.
Mr Younger also warned that "hybrid warfare", which included cyber-attacks and subverting democracy, was becoming an "increasingly dangerous phenomenon".
"The risks at stake are profound and represent a fundamental threat to our sovereignty," he said. "They should be a concern to all those who share democratic values."
In his first public speech since taking up the post of "C", he warned of the impact of Russia's alliance with President Bashar al-Assad in Syria in casting all opponents of President Assad as terrorists.
"I believe the Russian conduct in Syria - allied with that of Assad's discredited regime - will, if they do not change course, provide a tragic example of the perils of forfeiting legitimacy," he said.
"In defining as a terrorist anyone who opposes a brutal regime they alienate precisely that group that has to be onside if the extremists are to be defeated."
He added: "We cannot be safe from the threats that emanate from that land unless the civil war is brought to an end."

The Islamic State group had exploited the situation in Syria to fortify its stronghold in the region and wage a war on the West, he told journalists at MI6 headquarters in London.
He added that IS, also known as Isil or Daesh, had a "highly organised external attack planning structure" which was plotting attacks against the UK and its allies "without ever having to leave Syria".
Describing the risks MI6 agents faced in the field, he said: "Encountering terrorism, some of our agents operate in the most dangerous and hostile environments on earth.
"They know that the result of being identified as an MI6 agent could be their death. But they do what they do because they believe in protecting their country - and religion - from the evil that Daesh and other terrorist organisations present."
The threat level for international terrorism in the UK has been severe - meaning an attack is highly likely - since August 2014.
There are five threat levels - low, moderate, substantial, severe and critical - set by MI5's Joint Terrorism Analysis Centre.

Bron: http://www.bbc.com/news/uk-38250432
Mijn mening: Dit artikeltje weet ons te vertellen dat volgens het nieuwe hoofd van M16 (Britse inlichtingen- en veiligheidsdiensten) de terroristische dreigingen op het VK ongekend zijn. Dat is niet het enige probleem. Ook de cyberaanvallen en het willen ondermijnen van de democratie zijn problemen die de laatste jaren meer en meer opduiken. Het wordt een steeds gevaarlijker fenomeen. Uiteraard, ben ik het hiermee eens. Deze situaties stellen niet niets voor uiteraard. Het is ook moeilijk om voor zulke situaties oplossingen te vinden aangezien ze net zoveel voorkomen en zo moeilijk oplosbaar zijn. Hij gaat er ook vanuit dat de alliantie van Rusland (Putin) en Syrië (Assad) geen lachertje zijn. Dit baart mij ook zorgen. Het zijn 2 grote landen met grote aantallen van (kern)wapens etc. Wanneer zij tezamen zouden werken om een land zoals het Verenigd Koninkrijk te belazeren zal dit niet lang duren. Vandaar hoop ik dat het natuurlijk niet zal gebeuren, maar die kans is reëel. Zoals Alex Younger zei; "We kunnen niet veilig genoeg zijn voor bedreigingen, tenzij de burgeroorlog tot een einde wordt gebracht." Zo denk ik er ook over.