In 2011, Saudi Arabia awarded the contract worth €6.8 billion($7.2 billion) to a consortium of 12 Spanish companies and two Saudi firms to build the railway linking Islam’s holiest cities, Mecca and Medina.

Spanish prosecutors opened an investigation into the deal after a former mistress of Spain’s former king Juan Carlos was heard in a telephone conversation discussing commissions which were allegedly paid to secure the contract.

Anti-corruption prosecutors decided to shelve the probe “as it was not possible to determine the possible commission of the criminal offence”, according to the ruling dated May 4th.

The information which was gathered is “clearly insufficient”, and was “in part contradictory”, it added.

Juan Carlos was the target of a separate probe over the high-speed railway contract.

The investigation centred on $100 million Saudi Arabia’s late King Abdullah deposited into a Swiss bank account in 2008, to which Juan Carlos had access.

Prosecutors dropped the probe in March, saying the could not establish “any link” between the receipt of the money and the awarding of the contract.

Swiss prosecutors had also opened a probe into the same issue in 2018 but dropped the case in December for lack of evidence.

Saudi Arabia opened the 444-kilometre (275-mile) railway to the public in October 2018. It has improved transport connections between Mecca and Medina during the annual haj pilgrimage.

Spanish construction and engineering firm OHL, train maker Talgo and state track operator Adif were among the firms which made part of the consortium that built the railway.