The Saudi Arabian government awarded $22.5 billion in contracts to three foreign-led consortia on Sunday for the design and construction of a metro rail system in the capital Riyadh.

The project, which will involve six rail lines extending 176 kilometers (110 miles) and carrying electric, driverless trains, is the world's largest public transport system currently under development, Saudi officials said.

U.S. construction giant Bechtel Corp heads a group which won a $9.45 billion contract to build two lines, the government announced.

A consortium led by Spain's Fomento de Construcciones y Contratas won a $7.82 billion contract for three lines, while Italy's Ansaldo STS heads a group that won a $5.21 billion order.

(Reporting by Marwa Rashad, Writing by Andrew Torchia; Editing by Diane Craft)