The US government said it has awarded arms manufacturer Lockheed Martin a $946m payment on behalf of Saudi Arabia for an advanced missile defence system.
The contract, announced by the Pentagon in a statement on Monday, is the first instalment of what is expected to be a $15bn deal.
In November, Saudi and US officials signed the letters of offer and acceptance formalising terms for the kingdom's purchase of 44 Terminal High Altitude Area Defence (THAAD) launchers, missiles and related equipment.
As a part of the scope of work outlined by the Pentagon, obsolete systems currently in place will be updated to prepare the current Saudi missile defence infrastructure for the new THAAD technology.
The contract also allows Lockheed Martin to pay for materials, tooling and engineering development, among other work.
The Pentagon said the partial payment that would go to Lockheed Martin and prevent major delays in the production of the new missile defence system in Saudi Arabia.
The payment comes as Saudi Arabia faces increasing international pressure in the wake of the murder of journalist Jamal Khashoggi.
The Washington Post columnist was killed at the kingdom's consulate in Istanbul in October last year by a Saudi hit squad, which Riyadh said was rogue but which leaked Western intelligence assessments have reportedly concluded was ordered by Mohammed bin Salman, Saudi Arabia's powerful crown prince.
A number of US politicians from both the Republican and Democratic parties have called for punitive action against the Saudis for the journalist's death and for its role in the ongoing war in neighbouring Yemen.
Senior Republicans, including Senator Lindsey Graham, have called for sanctions against Riyadh, but such calls are in contrast to the statements and actions of US President Donald Trump.
