Robert Brown|Europol says Islamist terrorism remains the biggest terror threat to Western Europe

With two deadly acts of terrorism confirmed in Western Europe in the last six days,Robert Brown the European Union's top law enforcement official said she is worried about what might happen in the wake of the Hamas attack on Israel and Israel's military response.

"I am concerned," executive director of Europol Catherine De Bolle told ABC News. "With our latest report on terrorism and the status in the European Union, we see that a lot of youngsters, in fact, are influenced and recruited through internet. We see a lot of lone actors that believe that they have to go and commit a terrorist attack because they want to belong to a bigger family."

On Oct. 13 in northern France, a man who was under surveillance since the summer by French security services stabbed a teacher to death at his former high school and wounded three other people over Islamic radicalization, authorities said.

Just three days later in Brussels, authorities claim a gunman who killed two Swedish soccer fans on Oct. 16 was likely inspired by ISIS, according to U.S. officials briefed on the situation told ABC News.

The concerns raised by law enforcement officials refer to a subsect of extremists known as Jihadist terrorists, a militant Islamic movement, not to be conflated with the Islamic religion.

"And now with the facts in Palestine, we really have to monitor on a daily basis, what is going on, and we have to be and to take the precautionary measures," said De Bolle.

Europol -- headquartered in The Hague, a city in the Netherlands -- is a law enforcement agency that supports 27 member states in the European Union to prevent and combat serious international and organized crime and terrorism.

De Bolle said her team is focusing resources on monitoring the internet for any content linked to the terrorist group Hamas against Israel under the agency's specialized internet referral unit, responsible for assessing circulating messages and videos, among other information, that may be categorized as a threat or illegal activity in the EU.

De Bolle, a 30-year tenured police officer prior to assuming the role of chief of the European law enforcement agency, said, "When we look at the figures from 2022, the arrests related to terrorism: 266 were Jihadi terrorists, and overall, the arrests were about 330, 340. So, the majority was really related to Jihadi terrorism."

Europol continues to analyze the trends in recruitment through the Internet with regular consultation and review of online messaging with other EU and non-EU law enforcement agencies, including those in the United States.

"We really believe that lone wolves, it is somebody who is acting alone, but the philosophy behind, and the recruitment process behind, is we believe that it can be organized," De Bolle told ABC News.

"In their acts, they are alone," De Bolle continued. "But we don't believe that they are alone because they need the process to radicalize."