Fourteen people arrested in Belgium on suspicion of plotting to free a convicted al-Qaeda member from jail have been released without charge.
Security has been reinforced in public places
The suspects were released for lack of evidence after 24 hours in custody.
They were suspected of plotting to free Tunisian national Nizar Trabelsi, jailed in Belgium in 2003 for planning to attack US targets.
In spite of the releases, the interior ministry said heightened security measures would remain in place.
The federal prosecutor's office said searches at suspects' homes had yielded no explosives, weapons or other evidence to persuade the court to keep them in jail.
"According to our investigation there were sufficient indications pointing to a terrorist threat; that is why we did not wait to detain the suspects," Lieve Pellens, a spokeswoman for the prosecutor's office told the Associated Press.
She added that unlike some other European countries, Belgium does not have anti-terrorist laws which allow suspects to be held for longer than 24 hours.
Bin Laden associate
The arrest of the 14 men were announced on Friday by federal prosecutors and officials from the country's crisis co-ordination centre, at a hastily arranged news conference.
Tunisian, 37, played football for several German teams
Arrested in September 2001 in Belgium for plotting attacks on US targets
Sentenced to maximum 10 years in prison in 2003
Planned to attack Kleine Brogel air base where US military personnel stationed
Testified he intended to kill American soldiers
Following the arrests, security was stepped up at public sites including airports, subway stations and Christmas markets.
In spite of the releases, interior ministry officials said the measures would remain in place until 2 January.
Trabelsi, who used to play professional football in Germany, was jailed for 10 years in 2003 for planning to blow up a military base in Belgium housing US soldiers.
The trial heard that Trabelsi had met al-Qaeda leader Osama Bin Laden several times in Afghanistan and asked to become a suicide bomber.
He said he was ordered to go to Belgium, pack a bomb into a lorry and blow it up - with himself at the wheel - next to the canteen of the Kleine Brogel military base about 100 miles (160km) from Brussels.
But Trabelsi was arrested in Brussels two days after the 11 September 2001 attacks on the United States.