Dogged by controversy at home, US President Donald Trump has opened a nine-day foreign trip in Saudi Arabia, looking to shift attention from a spiralling political firestorm over his dismissal of former FBI director James Comey last week.

Key points: US President Donald Trump has arrived in Saudi Arabia — it is his first foreign trip since taking office

US President Donald Trump has arrived in Saudi Arabia — it is his first foreign trip since taking office The trip has been overshadowed by a week of controversies

The trip has been overshadowed by a week of controversies Mr Trump and the Saudi King are expected to sign a $US100b deal for Saudi Arabia to buy American arms

With delicate diplomatic meetings facing him, including three summits, Mr Trump faces a challenge of advancing his "America First" agenda without alienating key allies during his first trip abroad.

Stepping off Air Force One in 38 degrees Celsius heat with his wife Melania, Mr Trump and his entourage received a red-carpet welcome from Saudi King Salman.

The trip has been billed by the White House as a chance to visit places sacred to three of the world's major religions while giving Mr Trump time to meet with Arab, Israeli and European leaders.

But uproar in Washington threatened to cast a long shadow over the trip. His firing of Mr Comey and the appointment of a special counsel to investigate his campaign's ties to Russia last year has triggered a stream of bad headlines.

The New York Times reported Mr Trump had called Mr Comey a "nut job" in a private meeting last week in the Oval Office with Russian Foreign Minister Sergei Lavrov and ambassador to the United States Sergei Kislyak.

The White House did not deny the report, but said the "the real story is that our national security has been undermined by the leaking of private and highly classified conversations".

'Do you spend a lot of time in New York?'

Mr Trump and the King seemed at ease with each other, chatting through an interpreter.

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The two leaders sat side by side in the VIP section of the airport terminal and drank coffee served in the traditional Arab style.

"Do you spend a lot of time in New York?" Mr Trump was overheard asking the King.

The President was later honoured with Saudi Arabia's highest civilian honour — The Collar of Abdulaziz Al Saud. The medal, given to Mr Trump for his efforts to strengthen ties in the region, has also been bestowed upon Russian Presdient Vladimir Putin, British Prime Minister Theresa May and former US president Barack Obama.

Mr Trump's decision to make his first official trip abroad to Saudi Arabia, followed by Israel, countries which both share his antagonism towards Iran, marks a contrast with his predecessor's approach.

Mr Trump's criticism of the nuclear deal Iran reached with the US and five other world powers in 2015 pleases both Saudi Arabia and Israel, who accused Mr Obama of "going soft" on Tehran.

Poll results showed on Saturday that Iranians had emphatically re-elected President Hassan Rouhani, architect of Iran's still-fragile detente with the West.

Billboards advertising the visit read "together we prevail". ( Reuters: Jonathan Ernst )

Billions in US-Saudi deals to be signed

After a royal banquet, Mr Trump and the King were to have private talks and participate in a signing ceremony for a number of US-Saudi agreements, including a $US100-billion deal for Saudi Arabia to buy American arms.

National oil giant Saudi Aramco expected to sign $US50 billion of deals with US companies, part of a drive to diversify the kingdom's economy beyond oil exports, Aramco's chief executive Amin Nasser said.

Donald Trump receives the Collar of Abdulaziz Al Saud. ( AP: Evan Vucci )

Mr Trump is to deliver a speech on Sunday aimed at rallying Muslims in the fight against Islamic militants in Riyadh on Sunday.

A senior official also revealed the kingdom will unveil a digital centre with the purpose of monitoring the activities of Islamic State and other Islamist militant groups. The centre will open on Sunday, coinciding with Mr Trump's visit.

Mr Trump will also attend a summit with Gulf leaders as part of the six-nation Gulf Cooperation Council.

Saudi Arabia's King Salman bin Abdulaziz meets with US President Donald Trump during a reception ceremony. ( Reuters: Jonathan Ernst )

Travel a welcome distraction from Comey controversy

The uproar over Mr Comey's firing was unlikely to go away.

"It's almost always true that when a president goes on a big foreign trip, especially one that has some important summits … that that dominates the news and knocks most other stuff out," Republican strategist Charlie Black said.

Mr Trump, who has expressed a desire for friendlier relations with Moscow, drew a storm of criticism this week when it emerged that he had shared sensitive national security information with Russia's Mr Lavrov during a meeting last week in the White House.

The President was already under attack for firing Mr Comey in the midst of an FBI probe into Russia's role in the 2016 election and possible collusion with Trump campaign members.

"He clearly did have a bad two weeks. And clearly it's my hope that he does … right the ship, that he improves so that we can just get going," Republican House Speaker Paul Ryan said on the Hugh Hewitt radio show on Friday.

Sorry, this video has expired Donald Trump treated "unfairly" by media

Reuters