Donald Trump has opened his first presidential foreign trip in Saudi Arabia and won a warm reception while looking to shift attention from a political firestorm over his firing of former FBI Director James Comey.
Saudi King Salman bin Abdulaziz greeted him on a red carpet as he stepped off Air Force One on Saturday, shaking the hand of his wife, Melania, and riding in the US presidential limousine.
It was a warmer welcome than had been granted to Trump's predecessor, Barack Obama, who was seen in the Arab kingdom as soft on Iran and hesitant on Syria.
Trump's trip to Saudi Arabia, Israel, Italy, the Vatican and Belgium has been billed by the White House as a chance to visit places sacred to three of the world's major religions, while giving Trump time to meet with Arab, Israeli and European leaders.
But uproar in Washington cast a long shadow over the trip.
The president's firing of Comey and the appointment of a special counsel to investigate his campaign's ties to Russia last year have triggered a stream of bad headlines.
The New York Times reported Trump had called 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 real story is that our national security has been undermined by the leaking of private and highly classified conversations".
In another development, the Washington Post said a current White House official close to Trump was a significant "person of interest" in the investigation into possible ties between Trump's presidential campaign last year and Russia.
Trump and King Salman seemed at ease, chatting through an interpreter. At the royal al-Yamama palace, the king decorated Trump with the King Abdulaziz medal, the country's top civilian honour.
The two leaders exchanged tweets, Trump saying it was great to be in Riyadh and King Salman welcoming him.
"Mr. President, your visit will strengthen our strategic cooperation, lead to global security and stability," King Salman said in a message on his official Twitter account in Arabic and English.
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 Obama's approach.
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 Obama on "going soft" on Tehran.
Poll results showed on Saturday Iranians had emphatically re-elected President Hassan Rouhani, architect of Iran's still-fragile detente with the West.
After a royal banquet, Trump and the king were to have private talks and participate in a signing ceremony for a number of US-Saudi agreements, including a $US100 billion ($A134 billion) deal for Saudi Arabia to buy American arms.
National oil giant Saudi Aramco was expected to sign $US50 billion of deals with US companies on Saturday.
