More than 200 terror attacks were planned, thwarted or carried out in Europe last year as the continent faced a mounting threat from violent extremism.
There were 211 "failed, foiled or completed" terrorist strikes reported by six member states - with the highest number logged by the UK, according to Europol.
Some 151 people died and more than 360 were injured as a result of terrorism - with the vast majority of fatalities in France, which was hit by the Charlie Hebdo and Paris atrocities in 2015.
The figures are "markedly higher" than in 2014, when four people were killed and six wounded, Europol said.
The EU law enforcement agency's latest Terrorism Situation And Trend Report said the total number of terrorist incidents across the EU in 2015 slightly increased compared with 2014, when there were 201.
Denmark, France, Greece, Italy, Spain and the UK reported failed, foiled and completed attacks.
The report said the UK reported the highest number - 103. It is thought these were mostly linked to Northern Ireland.
The UK number did not specify terrorist affiliations, but figures for the other countries showed attacks specifically classified as separatist terrorism accounted for the largest proportion, followed by jihadist attacks. The report added that there was an increase in right-wing attacks.
Europol director Rob Wainwright said the EU experienced a "massive" number of casualties caused by terrorist attacks in 2015.
In a foreword to the report, he warned that Europe "currently faces a shifting and increasing range of threats emanating from jihadist groups and individuals".
Mr Wainwright said: "The so-called Islamic State has demonstrated its ability to strike at will, at multiple times and at a diverse range of targets.
"It has shown its prominence within the 'global jihad', while the threat posed by other jihadist militant groups has not diminished."
He said the overall threat is "reinforced" by substantial numbers of returned foreign terrorist fighters that many member states now have on their soil.
It was revealed earlier this year that around 850 people linked to the UK and regarded as a security threat are believed to have taken part in the Syrian conflict, with just under half thought to have returned to the country.
Mr Wainwright added that "another worrying development" is "the significant rise in nationalist (xenophobic), racist and anti-Semitic sentiments across the EU, each resulting in acts of right-wing extremism".
The 60-page assessment said most jihadist terrorist acts that took place in the EU in 2015 were performed in the name of Islamic State.
It warned that it is a "highly challenging task" for security services and law enforcement authorities to prevent every planned terrorist attack by keeping track of the "ever-increasing numbers of people suspected of being, in one way or another, sympathetic to IS ideology, and to focus their attention for unspecified lengths of time on those who might be willing and able to perform violent acts".
The report also said:
:: A significant percentage of all foreign "terrorist travellers" in Syria/Iraq are now female;
:: There is no concrete evidence to date that terrorist travellers systematically use the flow of refugees to enter Europe unnoticed;
:: In 2015, a total of 1,077 individuals were arrested on suspicion of terrorism-related offences - compared with 774 in the previous year.
The threat from international terrorism in the UK is currently assessed as severe, indicating that an attack is highly likely.