THE HAGUE, Netherlands — The number of people killed in attacks by extremists throughout Europe soared in 2015 from a year earlier, the European Union police agency reported Wednesday as it warned the Islamic State group may “put more emphasis on operations abroad” as a Western military alliance puts it under pressure in Syria and Iraq.

The Europol report painted a worrying picture of an EU assailed by Islamic extremist threats that are unlikely to recede anytime soon. It warned that Syrian asylum-seekers could be targeted and swiftly radicalized by IS recruiters while a new generation of fighters is being raised in IS territory in Syria and Iraq.

The report also stated that IS appears to favor attacks against soft targets because they “instill more fear in the general public.” That threat was horrifically underscored by the Bastille Day truck attack in Nice, France, that left 84 people dead.

In a move that underscored the swiftly evolving nature of the extremist threat, Europol also issued a separate statement on recent attacks in Nice, Germany and the United States, saying they “highlight the operational difficulties in detecting and disrupting lone actor attacks.”

The report was published on the day that senior government officials from the international coalition against IS were due to meet in Washington, DC, to discuss their campaign.

Compiling data from EU member states, Europol said that in 2015, 151 people died — up from four the previous year — and more than 360 were injured as a result of terrorist attacks in the bloc. All but one of the fatalities were the result of jihadi attacks, Europol said.

Six EU member states faced a total of 211 failed, foiled or completed terrorist attacks from jihad groups and other extremists. Law enforcement officials arrested 1,077 people for terrorism-related offenses.

The report also documented other extremist groups active in the EU, including separatists in Spain and Northern Ireland and extreme right-wing groups.

It warned of a potential new wave of fanatics as a result of children of “foreign terrorist fighters living with their parents in IS-held territory.

“IS has often shown that they train these minors to become the next generation of foreign terrorist fighters, which may pose a future security threat,” the report said.

While Europol said there was no concrete evidence of foreign fighters systematically sneaking into Europe among the huge flow of refugees in 2015, there is a “real and imminent danger” that members of the Sunni Muslim refugee community will “become vulnerable to radicalization once in Europe, and … be specifically targeted by Islamist extremist recruiters.”

The Hague-based police agency also reported that extremists are increasingly adept at using the internet and social media to spread propaganda, raise funds, potentially carry out cyberattacks and finance their operations by soliciting donations in closed forums and websites and even exploiting crowdfunding sites.