By Robert-Jan Bartunek
BRUSSELS (Reuters) - Belgian police raided suspected Islamist militants, mostly of Chechen origin, on Monday but found no evidence to confirm suspicions that they were planning an attack, prosecutors said.
The police carried out 21 coordinated raids as part of investigations of two groups of suspects.
One group, in or near the university city of Leuven, were suspected of plotting an attack, while a second group located on the Belgian coast was thought to include people who had returned from fighting in Syria, prosecutors said.
"The different raids have not so far produced evidence to confirm initial indications that an attack was being prepared in Belgium," prosecutors said in a statement.
Prosecutors said initially that 16 people had been detained.
But in a later statement, they said that two people from the group believed to have connections with the Syrian civil war had been placed under formal arrest. The remaining suspects were freed after questioning.
Prosecutors began investigating a suspected plot in January, after intercepting communications on the mobile messaging service WhatsApp with the help of U.S. authorities.
The investigation into the coastal group began in February after a person suspected of joining jihadist fighters in Syria returned to Belgium wounded to seek medical treatment.
Prosecutors said they had carried out the coordinated action because of contacts between the two groups, whose members were believed to have trained in Syria, Chechnya and Afghanistan.
In January, Belgian police killed two men who opened fire on them during a series of raids against an Islamist group that federal prosecutors said was on the point of launching attacks across the country.
Prime Minister Charles Michel praised the work of police and justice departments. "We will not allow any place in our democracy for those people who represent a menace for our citizens," he said.
(Additional reporting by Clement Rossignol, Adrian Croft, Philip Blenkinsop; Editing by Kevin Liffey)