Spain has ordered properties to be seized and bank accounts frozen in a money laundering investigation linked to the family of Rifaat al-Assad.
Judiciary officials said that the uncle of Syria’s President Bashar al-Assad was handed $300m of public money when he was sent into exile in 1984.
Now aged 79, he was placed under formal investigation in France last year.
Some of his fortune ended up in property in Marbella and Puerto Banus on the south coast, officials said.
While his brother Hafez al-Assad was in power, Rifaat was renowned for the brutality with which he crushed an uprising in the Syrian city of Hama in 1982. Last year he was said to be living in Paris.
He is under investigation in France for concealing stolen assets, money laundering and fiscal fraud. Several luxury properties have already been seized by French authorities in Paris and an appeal by the exiled former vice-president was turned down.
Rifaat al-Assad has in the past said he was given the money by the Saudi royal family.
Why have Spanish authorities acted now?
The general council of Spain’s judiciary said it was acting after French investigators found that part of his fortune had ended up in property in the Marbella area, under the name of companies managed by his wives and two of his children.
In a statement (in Spanish), it said that 15 properties search orders had been carried out, mainly in Puerto Banus on the Costa del Sol. While the bank accounts of 16 individuals linked to the exiled Syrian were being blocked, another 76 accounts were also affected.
Investigators said in total 503 properties linked to the family had been found, ranging from car parks to holiday homes, flats and a luxury hotel. Their total value was put at €691m (£590m; $735m) and all had been seized, they said.
One of the properties was a large farm called La Máquina worth an estimated €60m.