French Interior Minister Nicolas Sarkozy has denied a report that police intelligence officers were spying on an adviser working for his political rival Ségolène Royal.
The satirical weekly Le Canard Enchainereported that domestic intelligence agents had been asked to investigate Bruno Rebelle, a former Greenpeace spokesman who recently joined Ms Royal's team as an environmental adviser.
Mr Sarkozy is the ruling centre-right UMP's candidate for the April presidential election. In his job as interior minister he is also in charge of the country's police.
Mr Sarkozy and Ms Royal are the two leading candidates in the presidential race, and mudslinging between their two camps has intensified since the UMP officially picked Mr Sarkozy as its candidate on January 14.
"It's [the report] completely ridiculous. They must hold their nerve and stay calm," Mr Sarkozy said.
The newspaper said three officers had been asked to look into Mr Rebelle's background. It said the special branch had also been asked to look into other figures.
Francois Hollande, the Socialist party leader and Ms Royal's partner, demanded an urgent inquiry into the report.
"If this information is confirmed, and I ask that there be an immediate investigation, it would be extremely worrying because it would mean that the Interior Ministry is, after all, working for candidate Sarkozy," he said.
Recent opinion polls show Mr Sarkozy has pulled ahead of Ms Royal in the presidential race.