European terror attacks alarm US intelligence: NYPD

United States intelligence and police officials are alarmed by two unrelated terror attacks in Europe last weekend and what those attacks say about the current threat environment in the U.S., according to a New York Police Department briefing obtained by ABC News.

"There is no initial indication that the two attacks are linked, however, both incidents underscore the current complex and elevated terrorism/targeted violence threat environment as well as the persistent challenge of low-tech tactics being used against vulnerable targets, including public gatherings and houses of worship," the briefing said.

The attacks cited in the report include a deadly stabbing in Germany and an arson attack on a synagogue in France.

In Germany, a lone offender, armed with knife, indiscriminately stabbed civilians at a music festival on Aug. 23. Three people were killed in the attack and eight others were injured. ISIS claimed responsibility, and a 15-year-old boy was arrested, though it's unclear exactly how closely related he was to the terror group.

In France, an individual carried out an arson on a vehicle near a synagogue on Aug. 24, followed by an attempted attack on the building itself.

The prosecutor's office said two cars were set on fire on the grounds of the synagogue, one of which contained a gas bottle, causing an explosion. One police officer suffered injuries. A suspect was arrested after a firefight with law enforcement.

"While there are no early indications that these two attacks -- which occurred in different countries, focused on separate targets, and leveraged distinct low-tech tactics -- are related, they nevertheless underscore the complex and dynamic threat landscape which is comprised of malicious actors from across the ideological spectrum and exacerbated by tense global flashpoints, including the ongoing Israel-Hamas war," the document said.

The NYPD said the attacks will likely resonate with malicious actors, "serving as tactical/targeting inspiration for follow-on acts of terrorism and targeted violence."

ABC News' Felix Franz, Nadine El-Bawab, Jon Haworth and Victoria Beaule contributed to this report.