WASHINGTON • The abortive bombing by an ISIS-inspired Bangladeshi in New York has raised fresh fears of a possible surge in attacks during the year-end holiday season on both sides of the Atlantic.
Akayed Ullah, a 27-year-old immigrant who mainly injured himself when he tried to detonate a pipe bomb in a New York subway on Monday, reportedly told investigators that he targeted the station based on the Christmas posters on the walls.
The explosion, in which three others were lightly injured, came two weeks before Christmas, a period that terror experts say offers militants a large choice of "soft targets" where many people gather to shop and celebrate, with limited ability by the authorities to protect them.
Militants inspired by the Islamic State in Iraq and Syria (ISIS) carried out two devastating attacks in Europe during the holiday season last year. In one, a Tunisian refugee drove a large truck into a crowd at a Christmas market in Berlin, killing 11 and injuring dozens more.
A week later, a militant shot dead 39 people at a New Year's Eve party at an Istanbul nightclub.
In November last year, French police also broke up a militant ring that was planning an attack on a Christmas market and Paris Disneyland in the weeks before the Dec 25 holiday.
This year, Christmas markets across the continent have a heavier police presence and more concrete blocks to prevent vehicle attacks.
The US State Department has issued an alert to travellers heading to Europe during the holiday season, reminding them of the Berlin and Istanbul attacks.
"Extremists continue to focus on tourist locations, transportation hubs, markets/shopping malls and local government facilities as viable targets," it said.
The United States authorities have also put out a general domestic warning over possible season-based attacks, said senior Department of Homeland Security official Christopher Krebs.
Analysts say there have not been any public directives from the authoritative media channels of ISIS, Al-Qaeda and related groups.
But for weeks, supporters have disseminated propaganda encouraging holiday-period attacks.
Site Intelligence Group, which monitors militant websites, has shown posters made to encourage Christmas attacks. In one, a Santa Claus is depicted standing next to a box of explosives looking over New York's Times Square, with the text: "We meet at Christmas in New York... soon."
Another depicts a European city with a warning in three languages: "Soon on your holidays."
Such propaganda underscores ISIS' move to become an online "virtual caliphate" after the successful campaign to break up its territory in Syria and Iraq over the past year.
Rather than plot attacks from a central command, it now seeks to guide lone attackers online.
"It is adapting its model, looking to inspire individuals operating overseas, rather than trying to direct and command and control them," US National Counterterrorism Centre director Nick Rasmussen said on PBS television on Monday.