BERLIN (AP) — German security officials said Thursday they had detained four people, one of them a 16-year-old, in connection with a suspected plan to attack a synagogue in the western city of Hagen.

The detentions took place on Yom Kippur, the holiest day in Judaism, and two years after a deadly attack in another German city on the Yom Kippur holiday.

“One of the four people was a teenager living in Hagen,” police spokeswoman Tanja Pfeffer in nearby Dortmund told The Associated Press. She declined to comment on a report by news magazine Der Spiegel saying the teenager was a Syrian national.

Without identifying sources, newsmagazine Der Spiegel reported that a foreign intelligence service tipped off German security officials abut the threat.

It said the teenager told someone in an online chat that he was planning an attack with explosives on a synagogue, and the probe led investigators to the 16-year-old, who lived with his father in Hagen.

The detentions Thursday were preceded by police searches of several homes in Hagen, police said.

The interior minister of the state of North Rhine-Westphalia, where Hagen is located, confirmed that there was an attack threat, news agency dpa reported.

Speaking to young police officers in the city of Cologne, Herbert Reul said: ”Your colleagues probably prevented" an attack.

On Wednesday afternoon, police had cordoned off the synagogue after receiving tips about a possible attack. Dozens of police officers secured the building overnight and were still on the scene Thursday morning.

The threat came as Jews were preparing for Yom Kippur, the holiest day in Judaism. Following the threat, a festive service planned for Wednesday night at the synagogue was canceled, dpa reported.

Hagen police said Wednesday night that they were in close contact with the Jewish community.

Two years ago on Yom Kippur, a German right-wing extremist attacked a synagogue in the eastern German city of Halle. The attack on is considered one of the worst anti-Semitic assaults in the country’s post-war history.

The attacker repeatedly tried, but failed, to force his way into the synagogue with 52 worshippers inside. He then shot and killed a 40-year-old woman in the street outside and a 20-year-old man at a nearby kebab shop as an “appropriate target” with immigrant roots.

He posted an anti-Semitic screed before carrying out the Oct. 9, 2019, attack in the eastern German city of Halle and broadcast the shooting live on a popular gaming site.

German Justice Minister Christine Lambrecht sharply condemned the foiled Hagen attack.

“It is intolerable that Jews are again exposed to such a horrible threat and that they cannot celebrate the start of their highest holiday, Yom Kippur, together," the minister said.