Saudi Arabia has reached an agreement with Lockheed Martin to purchase four Freedom-class Littoral Combat Ships worth US$6 billion.

The deal is a part of overall $110-billion foreign military sale, and is expected to be announced during President Donald Trump’s visit to Riyadh Saturday.

The US and the Saudi ministry of defence “designed and negotiated a package worth $110 billion,” vice-admiral Joseph Rixey, head of the Pentagon’s defence security co-operation agency, said Friday. “When completed, it will be the largest single arms deal in American history,” he added.

The $6-billion deal will include spares, training and other logistics items.

"The primary difference between the Freedom-class and the Saudi-variant is the lack of modular mission space found in the US version of the Littoral Combat Ship," the United States Naval Institute (USNI) said Friday.

The LCS was designed to counter small surface craft attacks, diesel submarine threats and asymmetrical mine threats, according to published reports. Modular mission space refers to a method to quickly and easily remove and replace specialized equipment used for different combat missions.

The US and Saudi Arabia will also sign a letter of agreement for about $500 million in what could become a $3.5 billion deal for as many as 48 CH-47 Chinook helicopters and related equipment built by Boeing. That sale was approved by the state department and congress in December, said an official.