Dutch authorities on Sunday Dutch cleared five of the 12 Somali men who were detained Christmas Eve on suspicion of preparing a terrorist attack in the Netherlands.
Prosecutors said they had no evidence of criminal involvement against the five men, but the investigation of the other seven was continuing.
They must decide by Tuesday whether to bring the remaining suspects before a judge or let them go.
The men were picked up in Rotterdam after a tip from intelligence services that an attack may be imminent. There was no information on the alleged target, although Rotterdam is one of Europe's biggest commercial hubs with a huge port and large oil and gas storage facilities.
Three of the detainees who had no valid residency permits were turned over to immigration police, prosecutors said. Two of them were residents of Denmark and the residency of the third was not established. Two Dutch residents were released.
On Friday, police raided an internet cafe, four homes and two motel rooms but found no weapons or explosives.
Authorities said they cannot know for sure if they prevented a terrorist assault, but they did not want to take any risks. "What we did is take away the threat that was formed by these people," prosecutor Gerrit van der Burg said Saturday on national television.
The weekend action was not enough to raise the general threat level set by the National Terrorism Coordinator, which remained at "limited." Authorities believe the Netherlands could be targeted by Islamic radicals because of the high-profile anti-Islam campaign by one of the country's most popular politicians, Geert Wilders.
The terrorist alert came one year after a Nigerian student, Umar Farouk Abdulmutallab, passed through Amsterdam airport on a flight for Detroit, where he allegedly tried to ignite explosives taped to his underwear as the plane was descending toward its U.S. destination.
Heightened nervousness about a terrorist attack, especially on holidays or important anniversaries like the Sept. 11, 2001 attacks in the U.S., has led to mistakes in the past. Three months ago, police arrested two Yemenis traveling from the U.S. on a request from U.S. law enforcement agencies who feared they were conducting a dry run for a terrorist attack. They were released two days later for lack of any evidence of a crime.
A few weeks later, a British man of Somali ancestry also was arrested while en route to Uganda after a tip from British authorities. He, too, was released without charge.