A 57-year-old Rotterdammer has been arrested in the Netherlands on suspicion of involvement in preparations for a terrorist attack in Denmark, the Telegraaf said early on Thursday afternoon.

The person was arrested on behalf of the Danish authorities and a number of suspects have also been picked up in Denmark in connection with the case, the paper said.

Danish prime minister Mette Frederiksen told reporters on the fringes of the EU summit in Brussels the situation was “as serious as it gets” but did not give further details.

The Danish authorities are due to give a press conference later on Thursday afternoon.

Two days ago the threat level in the Netherlands was raised to four, or substantial, which means there is a real likelihood of a terrorist attack taking place.

EU Home Affairs commissioner Ylva Johansson warned recently that Europe faces a “huge risk” of terrorist attacks during the holiday period because of fall out from the Hamas Israel war.