Investigators are searching the headquarters of France's far-right National Front as part of a fraud probe into the use of EU parliamentary funds — a move the party denounces as a "political operation" by the French government.

Investigators began searching party headquarters in Nanterre, outside Paris, on Wednesday, a day after going through documents of National Front co-founder Jean-Marie Le Pen, father of leader Marine Le Pen.

The search is part of an investigation into potential misuse of EU funds to pay assistants of the party's 23 lawmakers. Many of the assistants have official roles within the party beyond their parliamentary duties.

A party statement calling the affair "pitiful" said the search is a "political operation ... whose goal is to hinder, survey and intimidate the patriotic opposition."