Spanish police have seized £590m worth of properties belonging to the family of Bashar al Assad.
The raids took place in the Puerto Banus marina area of Marbella and other areas of the resort.
Hundreds of properties and businesses belonging to Rifaat al Assad, the uncle of the Syrian president, and his family were targeted, according to the Diario Sur newspaper.
The assets were worth €691m (£590m), a judicial source told the AFP news agency.
The operation follows a corruption investigation against Assad's uncle launched in France.
The AFP source said: "Judge Jose de la Mata is coordinating the judicial operation against Rifaat al Assad, uncle of the current president of Syria, for money laundering in Puerto Banus and Marbella."
Rifaat al Assad went into exile in 1984 after trying to overthrow his older brother, the late Syrian dictator Hafez al Assad.
Spanish justice authorities say Rifaat, now aged 79, was given $300m (£240m) of state cash at the time, which he used to buy real estate in France, Liechtenstein, Luxembourg and Curacao.
Madrid's government said Rifaat and his family now own 503 properties, including holiday villas and plush hotel apartments - almost all in and around Puerto Banus and Marbella.
One of them, La Maquina (The Machine) at Benahavis just outside Marbella, is an 8,000 acre estate worth an estimated £51m.
All have been seized, authorities said.
His family is also linked to other assets such as hotels, discos and luxury goods retailers, Malaga Hoy said.
Diario Sur said Rifaat is not based in Marbella but some of his children are.
At one of the buildings affected, Gray D'Albion, close to Puerto Banus seafront, various valuable items were seen being removed on Tuesday morning, the newspaper said.
Carpets, tapestries, a Hummer car, an Infinity car and two Mercedes were among the items taken away.
In addition to the seizures, the accounts of 16 people and dozens of other entities, including two of his wives and six of his children, have been frozen.