A record number of terrorist attacks were planned, foiled or carried out in European Union countries last year, with the UK reporting the highest number of attacks.
EU law enforcement agency Europol said there were 211 attacks in 2015, the highest since records began in 2006.
Of those, the UK had the highest with 103 attacks, thought mostly to have been in Northern Ireland.
More than half of arrests in the EU - 687 - were "for jihadist terrorism".
Of these arrests, 94% were later found guilty in court.
The failed, foiled and completed terrorist attacks were in six EU member states - Denmark, France, Greece, Italy, Spain and the UK.
A spokeswoman for Europol said it did not have a breakdown of the number of terror attacks that had actually been carried out in the EU.
France had the highest number of planned, foiled or completed attacks - 72 - followed by Spain with 25.
According to the agency's EU Terrorism Situation and Trend Report, there were more than 1,000 arrests for terrorism-related offences last year - 424 of which were in France.
In addition to the jihadist terrorism arrests, there were 67 for left-wing terror, 11 right-wing terror and 168 separatist. A further 144 arrests were unspecified.
Europol said 151 people died and more than 360 were injured in terrorist incidents last year.
In its report, Europol said: "As in previous years, the attacks specifically classified as separatist terrorism accounted for the largest proportion, followed by jihadist attacks."
Europol also said the report outlines two "worrying developments".
"The overall threat is reinforced by the substantial numbers of returned foreign terrorist fighters that many member states now have on their soil, and the significant rise in nationalist (xenophobic), racist and anti-Semitic sentiments across the EU, each resulting in acts of right-wing extremism."
Europol said there was "no concrete evidence to date that terrorist travellers systematically use the flow of refugees to enter Europe unnoticed".
However, it noted that two of the men who carried out the Paris attacks in November, which killed 130 people, entered the EU through Greece as part of the influx of refugees from Syria.
The report said nuclear power plants and nuclear weapon facilities in the EU "remain potential targets for terrorists", as does "the deliberate contamination of water supplies".
It added: "Explosive remnants of war and illicit trafficking in explosives from former conflict areas present a significant threat to the EU.
"Chemical facilities or companies, especially these perceived as having a low profile until recently, can become a vulnerable target.
"Terrorists prefer the use of conventional firearms and explosives because of their availability, simplicity and effectiveness."
Europol also described cyber terrorism as "high potential but currently low probability".