Greek police have arrested several people over alleged links to a suspected terror plot in Belgium.
One of the men is alleged to have been in contact with the cell in Verviers, Belgium, where a shootout with police left two suspects dead on Thursday.
However, Belgian officials late on Saturday said that two of those detained in Athens were not among those wanted over events in Belgium.
Europe is on high alert after Islamist gunmen killed 17 people in Paris.
More than 20 people have been arrested in Belgium, France and Germany.
Troops were deployed across Belgium on Saturday to guard potential targets.
Belgium launched a series of raids on Thursday evening on a group of suspected jihadists.
Guns, munitions and explosives, as well as police uniforms and a large amount of money, were all seized by police during the operation.
Prosecutors said the group had planned to kill police officers and they charged five people on Friday with "participating in the activities of a terrorist group".
Earlier on Saturday, Belgian media said authorities were seeking Abdelhamid Abaaoud, a 27-year-old Brussels resident of Moroccan origin suspected of being the ringleader of the jihadi cell, and in hiding in Greece.
Greek authorities were reported to have sent DNA samples to their Belgian colleagues for further investigation.
However, a spokesman for Belgium's federal prosecutor told Le Soir newspaper that two of those held in Greece were not among those suspected of being implicated in the suspected Belgian terror plot.
He refused to comment on whether Abdelhamid Abaaoud was among those held in Athens.
The Greek police said the names of several people had been passed to them in connection with the plot to check if they were in Greece, Reuters reported.
Uniformed soldiers could be seen outside Jewish schools and government buildings in Belgium on Saturday.
Defence officials said the nation's security threat level would remain raised at three - the second highest level - for at least week.
There are particular concerns about the return of young Europeans who have gone to fight in Iraq and Syria.
Belgium says up to 350 of its citizens have gone to fight in Syria and Iraq, the highest number per capita in Europe. About 100 have returned, and are being monitored by the intelligence services.
No link has been established between the terrorist plot in Belgium and last week's attacks in Paris which killed 12 people at the offices of satirical magazine Charlie Hebdo, a policewoman and four others at kosher supermarket.