Andrew Parker, the director-general of the British Security Service MI5, also warned against the threat posed by British-born, or so-called home-grown terrorists.
"There will be terrorist attacks in this country. The threat level is severe and that means likely," Parker told The Guardian.
"That sort of tempo of terrorist plot and attempts is concerning and it's enduring. Attacks in this country are higher than I have experienced in the rest of my career - and I've been working at MI5 for 33 years. The reality is that because of the investment in services like mine, the UK has got good defences. My expectation is that we will find and stop most attempts at terrorism in this country," he said.
The 54-year-old spy chief also revealed that UK police and intelligence services had foiled around 12 terror plots in the country since June 2013.
More From This Section
In comments to the daily after a rare address to the Royal Society's annual diversity conference recently, he said: "ISIS (The Islamic State group) is an enduring threat, here to stay, and is at least a generational challenge. MI5 and the intelligence agencies have good defences because of the investment made in our capabilities. We will find and stop most attempts to attack us, but not all."
He said: "Russia is at work across Europe and in the UK today. It is MI5's job to get in the way of that.
"It is using its whole range of state organs and powers to push its foreign policy abroad in increasingly aggressive ways - involving propaganda, espionage, subversion and cyberattacks."
According to Parker, under Vladimir Putin Russia seems to "define itself by opposition to the West and seems to act accordingly".
"Russia has been a covert threat for decades. What's different these days is that there are more and more methods available.