According to the U.S. State Department, the Syrian leader Bashar Assad's family is likely worth $1 billion-$2 billion, despite U.S.-led efforts to isolate him over the brutal war.

In a report required by Congress, the State Department said it could only provide an "inexact estimate" with the Assads believed to hold assets under fictitious names or through opaque property dealings.

"Estimates based on open-source information generally put the Assad family net worth at between $1billion-$2 billion," said the publicly released part of the report, some parts of it classified.

Quoting nongovernmental and media reports, the State Department said that the Assads run "a complex patronage system including shell companies and corporate facades that serves as a tool for the regime to access financial resources."

The estimate includes the leader's wife, brother, sister, cousins and uncle, most of whom are under U.S. sanctions. The State Department said it did not have enough information on the net worth of his three children, the youngest of whom is 17.

The U.S. Congress has led sanctions that aim to prevent a return to business as usual with Assad, who has regained control over most of Syria after a decade of war estimated to have killed nearly half a million people.

The United States has called for accountability after wide concerns about human rights. But much of the region is moving on, with Assad visiting the United Arab Emirates (UAE) in March in his first official visit to an Arab country since the war broke out.