Police in southern Spain have staged raids targeting assets of the extended family of the Syrian leader, Bashar al-Assad, a judicial source said.

The raids, in the Puerto Banús marina area of the plush resort of Marbella, are the result of a corruption investigation launched in France into Assad’s uncle, Rifaat al-Assad.

French and Spanish authorities have been cooperating on the case and Spain opened an investigation on the back of the one in France, where authorities suspect Rifaat al-Assad of misuse of Syrian public funds and money laundering.

In a written statement, Assad, 79, and his family retorted that they had “never benefited from financing that in any way wronged the Syrian state and its people”.

“They question the timing of these coordinated judicial actions, 33 years later, at a time when their country is suffering more than ever and where Rifaat al-Assad’s voice should be heard to contribute to find a peaceful solution to the Syrian conflict,” it read.

Madrid authorities say the Spanish investigation established that Rifaat al-Assad and his family had 503 properties in their portfolio, ranging from holiday villas to luxury hotel apartments – almost all in and around Marbella.

One residence, La Máquina at Benahavís just outside Marbella, is worth an estimated €60m (£51m).

The investigating magistrate has frozen 16 people’s bank accounts and a further 76 accounts in connection with the case, the judicial source said.

First charged in France last June, Assad holds €90m (£77m) worth of property assets in that country, including an office block in Lyon, investigators say.

He has previously said that much of his wealth comes from gifts bestowed by the Saudi royal family, which he claims gave him political backing in the 1980s.

Last October, Assad told French authorities that former Saudi kings Fahd and Abdullah had provided those gifts, according to a source close to the French investigation.

Assad insists he does not keep close tabs on his property holdings.

The initial investigation was triggered by an activist group which represents victims of financial crime.