The head of MI5 is warning that the Islamic State group aspires to commit “devastating” and “more complex” attacks in Europe after losing territory in the Middle East.
Director general Andrew Parker will make the warning at a meeting of European security chiefs in Berlin.
He will also condemn Russia for the “targeted” Salisbury poisoning.
And he will reveal that 12 terror attacks have been stopped in the UK since the Westminster attack in 2017.
Mr Parker’s speech comes after one person was killed and four others injured by a knifeman in Paris on Saturday. The attack was claimed by IS.
In December last year, Mr Parker reported that nine terrorist attacks had been prevented by the security services and police in 2017.
Monday’s updated total brings the number of disrupted attacks in the UK to 25 since 2013.
In his speech, the chief of the security service will say he is “confident about our ability to tackle these threats, because of the strength and resilience of our democratic systems, the resilience of our societies and the values we share with our European partners”.
Mr Parker will also accuse the Kremlin of “flagrant breaches of international rules” over the poisoning of a Russian ex-spy and his daughter in Salisbury in March.
Former double agent Sergei Skripal and his daughter Yulia were exposed to a nerve agent belonging to the Novichok group.
The Russian government has denied any involvement in the 4 March attack, but has been the subject of condemnation and diplomatic sanctions from the West.
Mr Parker will describe the attempted assassination of the Skripals as a “deliberate and targeted malign activity” which risks Russia becoming a “more isolated pariah”.
He will condemn Moscow by calling for the need to “shine a light through the fog of lies… out of their propaganda machine”.
Mr Parker will add that European intelligence agencies must rely on “shared co-operation more than ever”.
And he will thank European security services for their support in the investigation into the Manchester bombing last year.
“European intelligence cooperation today is simply unrecognisable to what it looked like five years ago,” he will say.