Leaked Panama Papers seen by French daily Le Monde reveal Syria's regime has been able to circumvent international sanctions and fund its war effort through shadow companies.

Three Syrian companies, Pangates International, Maxima Middle East Trading and Morgan Additives Manufacturing, used the services of Panama-based law firm Mossack Fonseca to create shadow companies in the Seychelles, reported the newspaper on Tuesday. Le Monde, a partner in the year-long worldwide media investigation into a trove of 11.5 million documents leaked from Mossack Fonseca, said the shadow companies were "a way for the Syrian regime to circumvent international sanctions imposed since the start of the war".

The three firms are under US sanctions for allegedly providing petroleum supplies to President Bashar al-Assad's regime likely to be used by his military, including aviation fuel. Since the start of Syria's war in 2011, tens of thousands of people have been killed and thousands of homes destroyed in air raids and barrel bomb strikes.

Le Monde said the leaked documents show Mossack Fonseca continued to work with at least one of the companies, Pangates, until at least nine months after the sanctions were announced. Pangates belongs to the Damascus-based Abdulkarim group, which is close to the Syrian government. The probe, coordinated by the International Consortium of Investigative Journalists (ICIG), has exposed a tangle of financial dealings by global elites.

Assad's billionaire cousin Rami Makhlouf, who is facing sanctions, was also shown by the leaks as long having registered companies in tax havens. Syria's most notorious and powerful tycoon, Makhlouf founded shadow companies such as Drex Technologies SA, which was registered in the British Virgin Islands in 2000 and which it took Mossack Fonseca a decade to grow concerned about. In 2011, the law firm cut ties with Makhlouf, just after the outbreak of the revolt calling for Assad's ouster.

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Panama's state prosecutor's office has said it will launch an investigation into revelations contained in a massive data leak of a law firm that created offshore companies for the world's rich and powerful. "The facts described in national and international communication media publications under the term 'Panama Papers' will be the subject of criminal investigation," the office said in a statement on Monday.