Paris, France (CNN) -- The headquarters of French President Nicolas Sarkozy's political party have been searched by investigators as part of an ongoing investigation into the finances of L'Oreal heiress Liliane Bettencourt, a party spokesman said Thursday.
The hour-long search was carried out by three investigators Wednesday afternoon, said UMP spokesman Eric Cesari. The prosecutor's office in Nanterre, a Parisian suburb, also confirmed the search, but offered no other details.
They were seeking documents linking Sarkozy's campaign to alleged political contributions from Bettencourt, Cesari said, adding that the headquarters had gotten advance warning of the search.
"We have nothing to hide," Cesari said. He added that the investigators left without taking anything.
Police have also questioned Patrice de Maistre, a financial adviser to Bettencourt, and French Labor Minister Eric Woerth in recent months. The case centers on claims that de Maistre gave envelopes of cash to Woerth and Sarkozy, in some cases allegedly in violation of campaign finance laws.
Woerth and Sarkozy have both denied the allegations, which were made in secret recordings that surfaced in June.
The recordings, allegedly made by Bettencourt's butler, also refer to a Bettencourt bank account in Switzerland containing 80 million euros ($98.3 million), which had not been reported on her taxes. Bettencourt is France's richest woman.
Woerth's wife, Florence, was questioned in July. The secret recordings published in June revealed that she had been de Maistre's deputy until late June.
Bettencourt's former bookkeeper, Claire Thibout, elaborated on the allegations in an interview in July with a French investigative website.
She said she prepared envelopes of cash that were to be given to Sarkozy and Woerth, who previously worked in the Budget Ministry and was in charge of reforms to France's retirement system.
Thibout's lawyer told French news agency Agence France-Presse in July that de Maistre once asked his client for 150,000 euros ($188,800) and said he would give it "discreetly" to Woerth at a dinner.
Thibout testified before a judge about the allegations earlier in July.
The French newspaper Le Monde published her testimony, in which she said she regularly withdrew large sums of money at de Maistre's request.
Journalist Saskya Vandoorne contributed to this report