Venezuelans have not only been buying Spanish real estate, but also building it. In 2017, the Cohén family, owners of one of Venezuela’s largest commercial real estate companies, opened the Sambil Outlet on the outskirts of Madrid, which bills itself as Spain’s largest shopping mall.

The Cohéns are among the Venezuelans who moved to Spain around 2012, just as the government in Madrid was forced to negotiate a European banking bailout. The timing allowed them to pick up Spanish assets cheaply: Sambil replaced a mall that went bankrupt during Spain’s banking crisis.

This year, the Cohén group also bought a building in Salamanca that will be turned into a dozen luxury apartments. Among Salamanca’s other investors is Miguel Ángel Capriles, a relative of Henrique Capriles, a politician and leader of the opposition in Venezuela.

Amid mounting international pressure on Mr. Maduro, the Spanish authorities have been stepping up their efforts to monitor the inflow of Venezuelan money. It’s a difficult task, according to some lawyers, given that wealthy Venezuelans have always kept money overseas to offset capital controls and currency fluctuations.

“Spain has the obligation to control money inflows, but rich Venezuelans have long learnt that their savings should be in a strong currency, preferably in an overseas account,” said Juan Carlos Gutiérrez, a Venezuelan lawyer who moved to Madrid last December.

In fact, the most high-profile detention to date of a Venezuelan in Spain was the result of an arrest warrant issued by Mr. Maduro’s government: In April, the Spanish police detained Claudia Patricia Díaz, a former treasury official who was also a nurse to Hugo Chávez, the Venezuelan president who died in 2013; and her husband, a former security chief. The arrests were part of a money laundering case that included an investigation into the couple’s purchase of an apartment in Madrid in 2015 for €1.8 million, or about $2.1 million.