Several Hamas members and people suspected of planning terrorist attacks in Europe were arrested in Germany, Denmark and the Netherlands on Thursday, Reuters reports.

German prosecutors announced in a statement that four members of the terrorist group Hamas were detained on suspicion of planning attacks on Jewish institutions in Europe. The announcement came after Danish police said earlier Thursday that three people had been arrested in Denmark and one in the Netherlands on suspicion of planning a terrorist attack.

According to the German prosecutor’s office, three suspects were detained in Berlin, and another was detained in the Netherlands.

Nazih R, a Dutch national, was arrested by police in Rotterdam, while Abdelhamid Al A and Ibrahim El-R, of Lebanese origin, and Mohamed B, an Egyptian national, were arrested in the German capital.

According to prosecutors, all four were longtime members of Hamas and had close ties to the leadership of the group’s military wing. Hamas leaders in Lebanon tasked Abdelhamid Al-A with supplying weapons.

Hamas planned attacks on Jews in Germany

Prosecutors said the weapons were to be brought to Berlin and kept close at hand for potential terrorist attacks on Jewish institutions.

“Following the horrific attacks by Hamas on the Israeli population, attacks on Jews in Jewish institutions have also increased in our country in recent weeks,” German Justice Minister Marco Buschmann said in a statement regarding the detained suspects.

“Therefore, we must do everything possible so that the Jews of our country do not fear for their safety again,” he added.

European authorities have already warned of an increased risk of attacks by Islamists radicalized by the war between Israel and Hamas.

A terrorist attack was thwarted in Denmark

On the other hand, also on Thursday, Copenhagen police announced the arrest of three people in Denmark and one in the Netherlands on suspicion of preparing a terrorist attack. It is not known whether the arrests are related to the detention of Hamas members in Germany, but Danish police said the actions were the result of a coordinated cross-border police operation.

It is not yet known what the suspects’ motives were or whether they are connected to Islamist militants or far-right groups. Denmark’s security and intelligence agency PET said in August that the threat to Denmark had increased after anti-Islam activists burned several copies of the Koran over the summer.

“The investigation showed that a network of people was preparing a terrorist act,” said Flemming Dreyer, chief commissioner of PET, at a press conference in Copenhagen. “The arrests and raids we are carrying out today are based on an intensive investigation carried out by PET in close cooperation with our partners abroad,” he added.

Danish police said the raids were ongoing across the country and were being carried out at an early stage of the investigation. The network had ties to organized crime both in Denmark and abroad, including a gang called Loyal To Familia, or LTF, Dreyer said, but declined to elaborate on possible motives.

Police said they would increase their presence in public places in the coming days, particularly in Copenhagen and around areas with Jewish communities. Denmark’s Jewish community said it had been publicly informed of the raids but was unaware of specific threats to Jewish targets.

The Prime Minister of Denmark suggests that Islamist terrorists may have been behind the plot

“This is extremely serious,” Danish Prime Minister Mette Frederiksen told the Ritzau news agency at a meeting with EU leaders in Brussels. “It is, of course – with regard to Israel and Gaza – completely unacceptable for someone to bring a conflict from another part of the world into Danish society,” she said.

“For several years now, I have seen that there are people living in Denmark who do not wish us well. Which ones are against our freedom, and which ones are against Danish society and all that follows from that,” commented Frederiksen.

The PET service has been warning about possible attacks for more than a decade. Police said they had left the terror alert level unchanged at 4 on a scale of 1 to 5, reflecting a “significant” threat.

Police said the three arrested in Denmark will be charged with terrorism under the Criminal Code and brought before a judge for preliminary questioning.

Dutch police, in turn, said the 57-year-old man was arrested in Rotterdam on Thursday at the request of German authorities as part of a Danish-German investigation.

The Netherlands’ National Counter-Terrorism and Security Coordinator (NCTV) this week raised the country’s threat level to 4, meaning “significant,” on a 5-point scale, citing the conflict between Israel and Hamas.