Dutch police arrested three men on Monday suspected of planning an attack, it has emerged.
Prosecutors said the arrests in Rotterdam came after the Dutch intelligence service said it was possible the suspects aged 31, 32 and 39 were about to carry out an act of violence.
The Dutch government classes the risk of a terrorist attack as "limited", the second lowest in a four-stage warning system, cutting it from "substantial" last April.
In 2004 the Netherlands was shaken by the murder of filmmaker and Islam critic Theo van Gogh by a Dutch-Moroccan. Several other Muslim militants have since been sentenced for planning attacks on politicians and government buildings.
In neighbouring Belgium a two-week state of alert prompted by the uncovering of an apparent plot to free an al-Qaeda suspect from jail has been eased.
Security in Brussels was suddenly stepped up on December 21st after the arrest of 14 suspected Islamic militants. The 14 were released without charge the next day, but Brussels cancelled its traditional New Year fireworks display because of the perceived threat.
A Belgian court is due to give its verdict next week in the case of six men accused of trying to recruit suicide bombers.