PARIS, March 1 (Reuters) - A group of French people with thyroid ailments began legal moves on Thursday to try to prove they fell ill because France failed to warn citizens of the radioactive fallout of the 1986 Chernobyl nuclear disaster.

The 53 plaintiffs, backed by two pressure groups, lodged a complaint against persons unknown at the Palace of Justice in Paris on grounds of alleged poisoning and associated counts.

The technical step under French law means a judge must now examine the complaint, though the judge is not bound to order a criminal investigation.

A similar attempt by a sole plaintiff failed last year on grounds that the person could not demonstrate a scientific link between the Chernobyl accident and the illness.

The Chernobyl complex in Ukraine was the site of the world's worst nuclear accident in April 1986, when a reactor exploded and radiation spewed from its burning shell. The plant shut down for good in December.

The plaintiffs allege that French authorities did nothing to alert citizens to the potential dangers from a cloud of radioactivity that drifted west from Chernobyl.

"Too many things have been hidden. We were always told that the cloud had stopped at the border. We want the truth," said one of the plaintiffs, 50-year-old Jean-Claude Foures.

The lawyer for the group, Christian Curtil, acknowledged that there was no absolute scientific link between the accident and his clients' illnesses, but said there was sufficient circumstantial evidence to warrant opening an investigation.

06:50 03-01-01