The French authorities have seized a private jet said to belong to the family of ousted Tunisian President Zine al-Abidine Ben Ali.
It comes after three French NGOs filed a legal case against Mr Ben Ali over allegations of corruption.
Mr Ben Ali and his family built up significant assets during his 23 years in power.
On Monday, EU foreign ministers agreed to freeze his assets in response to a request by Tunisia.
Swiss officials have already frozen tens of millions of francs, and grounded a Falcon 9000 jet in Geneva.
Mr Ben Ali resigned and fled to Saudi Arabia on 14 December after weeks of anti-government protests.
French investigators said the jet was impounded at Le Bourget airport near Paris where it had been parked in a hangar for a week.
Officials said it belonged to the Mabrouk family, one of whose members is Mr Ben Ali's son-in-law, said the AFP news agency.
The investigation into the Ben Ali family assets began last week after Sherpa, Transparency International France and the Arab Commission for Human Rights launched a legal case accusing the former leader of corruption, misusing public funds and money-laundering.
They estimate the wealth amassed by the former leader and his entourage at £3bn ($5bn).
The family's interests are thought to include banks, insurance, fishing and construction as well as about 30 properties, including hotels.
Transparency International says the Trabelsi family of Mr Ben Ali's wife, Leila, could have properties in Paris, the Alps and the Cote d'Azur, with millions of dollars in bank accounts.
Tunisian prosecutors are also investigating the family's foreign assets, including possible illegal transactions and foreign bank accounts.
Some 33 members of Mr Ben Ali's family were held over claims that they had plundered the nation's resources.
Separately, France's Foreign Minister Michele Alliot-Marie has defended herself against accusations that she accepted a private flight from a close ally of Mr Ben Ali while protests were underway in Tunisia, French media report.
Ms Alliot-Marie's office acknowledged that she had taken a flight with Tunisian businessman Aziz Miled while on holiday, but denied that he was a part of the regime, saying he had suffered financially under Mr Ben Ali.