US aerospace giant Boeing Company has secured a contract valued at $4 billion to modernize the Royal Saudi Arabian Air Force's fighter jet fleet, according to the Pentagon.

The procurement order covers conversion of 68 existing F15S jets to the new F15S-A configuration.

The Pentagon said the work, expected to be completed by December 31, 2019, would be done at Robins Air Force Base in Georgia.

The contract also provides for four base stand-up kits, which include spares and support equipment needed to achieve operating capability for the fighter jets.

Altogether, about 150 new or converted F-15SA aircraft will be supported or maintained at four Saudi bases, according to information provided earlier by Robins. It is the largest foreign military sales contract to be filled the base.-Reuters