Police have arrested three people in co-ordinated actions across Denmark and one person was detained in the Netherlands on suspicion of plotting to carry out “an act of terror”, authorities said.

Danish officials have stopped short of indicating what the suspected terror plots were connected to other than saying the arrests in Denmark had “threads abroad” and were “related to criminal gangs”, singling out the banned, predominantly immigrant gang Loyal to Familia.

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

He did not provide more details.

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

In January that year, a Danish court upheld a nationwide police ban on the gang, saying it should be dissolved as illegal under Denmark’s constitution.

The gang had been behind feuds, violence, robberies, extortion and drug sales in the Danish capital and “had used violence and illegal means to achieve its goal”, the Copenhagen District Court said at the time.

In September 2018, police in Denmark issued a temporary ban against the gang and said anyone seen wearing its logo could face prosecution.

“Persons abroad have been charged,” Mr Drejer said.

“It is a serious situation.”

Speaking at a press conference, he added the arrests were “carried out in close collaboration with our foreign partners”, and said those arrested were part of “a network”.

Mr Drejer said the suspects would face a custody hearing within 24 hours, likely behind “double closed doors” – meaning that he could not give details about the case, any target or motive.

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

“It shows the situation we are in in Denmark. Unfortunately.”

“It is absolutely true when both (Denmark’s intelligence agencies) say that there is a high risk in Denmark,” Ms Frederiksen said.

“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.”

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

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 Israel, Prime Minister Benjamin Netanyahu’s office said that Denmark had arrested seven operatives who were acting on behalf of the Palestinian militant group Hamas, which runs the Gaza Strip, and thwarted an attack aimed at killing innocent citizens on European soil.

The figure of seven arrests was different from the number provided by the Danes and the discrepancy could not immediately be reconciled.

Mr Netanyahu’s office said Hamas, which has been labelled a terrorist organisation by the United States, the European Union and other Western countries, strives to hit targets around the world and in Europe in particular.

The statement added that Israel’s intelligence agencies “will continue to operate … in order to repel the intentions of Hamas and eliminate its capabilities”.

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”.