Britain can never be safe from Syrian terror threats until the brutal civil war is brought to an end, spy chief Alex Younger has said.
The "murderously efficient" Islamic State (IS) is currently plotting violent attacks against the UK from Syria despite being under military pressure, the head of MI6 warned.
In his first public speech since taking up the post of "C", Mr Younger said the scale of the terror threat is "unprecedented" as he highlighted how intelligence and security services have disrupted 12 terrorist plots in the country over the last three years.
Speaking to journalists at MI6 headquarters in London's Vauxhall, he attacked Russia for backing Bashar Assad's "discredited" Syrian regime, warning that defining opponents as terrorists alienated people who must be brought onside if extremists are to be defeated.
"The plight of the Syrians continues to worsen. I cannot say with any certainty what the next year will bring," he said.
"But what I do know is this - we cannot be safe from the threats that emanate from that land unless the civil war is brought to an end."
Mr Younger warned that "hybrid warfare", which includes cyber attacks and subverting democracy as well as more traditional methods of attack, was becoming an "increasingly dangerous phenomenon".
"The risks at stake are profound and represent a fundamental threat to our sovereignty. They should be a concern to all those who share democratic values."
IS, also known as Daesh, exploited Syria's civil war to bolster its stronghold in the region and wage a war on the West.
Mr Younger said the service must "take the fight to the enemy" by penetrating terror organisations.
"The scale of the threat is unprecedented. The UK intelligence and security services have disrupted 12 terrorist plots in the UK since June 2013. And MI5 and the police continue to run hundreds of investigations into those intent on carrying out or supporting terrorist atrocities against our citizens.
"As I speak, the highly organised external attack planning structure within Daesh, even as they face military threat, are plotting ways to project violence against the UK and our allies without ever having to leave Syria.
"We face a threat that exploits failed states within a connected world. So, we cannot pull up the drawbridge. Instead, we need to take the fight to the enemy, penetrating terrorist organisations upstream. By that I mean as close to the source as possible.
"In footballing terms, it's about always ensuring you are playing in the opponent's half."