Denmark and Germany have announced the arrests of several terror suspects, including alleged Hamas members suspected of plotting attacks on Jews and Jewish institutions in Europe over the ongoing Israel-Hamas war.

The announcements were issued separately and it was unclear how the arrests were connected and if they were the result of co-ordinated actions, or even possibly one operation spanning the continent.

Danish police said three people were arrested across Denmark while a fourth person was detained in the Netherlands on suspicion of plotting to carry out “an act of terror”.

Officials in Copenhagen did not provide any details beyond saying the arrests had “threads abroad” and were “related to criminal gangs”, singling out the banned, predominantly immigrant gang Loyal to Familia that had long been behind feuds, violence, robberies, extortion and drug sales in the Danish capital.

However, Flemming Drejer, the operative head of Denmark’s Security and Intelligence Service, cryptically said police had “a special focus” on Jewish institutions.

He said Denmark was not changing its terror threat level, which has been at “serious”, the second-highest level, since 2010.

“Persons abroad have been charged. … It is a serious situation,” Mr Drejer told a news conference, adding that the arrests were carried out in “collaboration with our foreign partners” and that those arrested were part of “a network”.

The suspects would face a custody hearing within 24 hours, he said, probably behind “double closed doors” – meaning he could not give any details about the case.

“This is extremely serious,” Danish Prime Minister Mette Frederiksen said on Thursday from Brussels where she was attending a European Union summit.

“It is of course completely unacceptable in relation to Israel and Gaza, that there is someone who takes a conflict somewhere else in the world into Danish society,” she added.

In the Netherlands, police said a 57-year-old Dutch man was arrested in the city of Rotterdam, based on a request from German authorities, according to spokesman Jesse Brobbel.

On Tuesday, the Dutch counterterrorism agency raised the country’s threat alert to its second-highest level, saying the possibility of an attack in the country is now “substantial”.

In Germany, authorities said three suspected members of the Palestinian militant Hamas group who were allegedly planning attacks on Jewish institutions in Europe were arrested on Thursday.

Two men were arrested in Berlin and one in the Dutch city of Rotterdam, while a fourth suspect was temporarily detained in Berlin, Germany’s federal prosecutor said.

Authorities only identified the men by their first names and the first initial of their last name, in line with German privacy rules.

The four were Abdelhamid Al A, born in Lebanon; Egyptian national Mohamed B; Dutch national Nazih R and Ibrahim El-R, born in Lebanon.

The authorities alleged three of the men “have been longstanding members of Hamas and have participated in Hamas operations abroad”.

They said the suspects were “closely linked to the military branch’s leadership” of Hamas, considered a terrorist organisation by the United States and the European Union.

German justice minister Marco Buschmann thanked the authorities for the arrests and said that “attacks on Jews and Jewish institutions have also increased in our country in recent weeks” due to the Israel-Hamas war.

It was not immediately clear if and how the Danish and the German arrests were connected.

In Israel, Benjamin Netanyahu’s office lauded what it said were seven Hamas suspects arrested in Europe, but attributed the arrests to Danish police.

The prime minister’s office said Denmark had arrested seven operatives acting on behalf of Hamas and “thwarted an attack aimed at killing innocent citizens on European soil”.

Mr Netanyahu’s office said Israel’s intelligence agencies “will continue to operate … in order to repel the intentions of Hamas and eliminate its capabilities”.

The discrepancies between the Danish, German and Israeli statements could not immediately be resolved.

Earlier this month, the European Union’s home affairs commissioner Ylva Johansson warned that Europe faced a “huge risk of terrorist attacks” over the Christmas holiday period due to the fallout from the fighting in Gaza.

Denmark’s foreign intelligence service, known as FE, said on Thursday in its annual assessment for 2023 that “the war between Israel and Hamas has once again shown that unresolved conflicts in Europe’s immediate area can escalate rapidly and create widespread regional instability”.