WASHINGTON • The United States is close to completing a series of arms deals for Saudi Arabia totalling more than US$100 billion (S$140 billion), a senior White House official has said, a week ahead of President Donald Trump's planned visit to Riyadh.

The official, who spoke on condition of anonymity, said the arms package could end up surpassing more than US$300 billion over a decade to help Saudi Arabia boost its defensive capabilities while still keeping US ally Israel's qualitative military edge over its neighbours.

"We are in the final stages of a series of deals," the official said.

The package is being developed to coincide with Mr Trump's visit to Saudi Arabia.

Mr Trump leaves for the kingdom on Friday, the first stop on his maiden global trip.

Reuters reported last week that Washington was pushing through contracts for tens of billions of dollars in arms sales to Saudi Arabia, some new, others already in the pipeline, ahead of Mr Trump's visit.

The US has been the main supplier for most Saudi military needs, from F-15 fighter jets to command and control systems worth tens of billions of dollars in recent years.

Mr Trump has vowed to stimulate the US economy by boosting manufacturing jobs. The Saudi package includes American arms and maintenance, ships, air missile defence and maritime security, the official said last Friday.

"We'll see a very substantial commitment... In many ways, it is intended to build capabilities for the threats they face."

While in Riyadh, the official said, Mr Trump would attend three major events: A series of meetings with Saudi officials, a separate session with leaders of the six-nation Gulf Cooperation Council and a lunch with Arab and Muslim leaders, 56 of whom have been invited, to discuss combating extremism and cracking down on illicit financing.

Mr Trump will also discuss how to counter the threat from Islamic State in Iraq and Syria militants, the war in Yemen and threats of ballistic missiles and maritime shipping in the Red Sea, the official said.

A major part of the agenda with Gulf leaders will be the Syrian civil war amid calls for "de-escalation zones" in Syria to provide a safe haven for Syrian refugees.

Besides Saudi Arabia, Mr Trump's first foreign trip will also take in visits to Israel, the Vatican, Brussels for a Nato summit and Sicily for a Group of Seven summit.

REUTERS