US President Donald Trump tells 50 Muslim leaders in Saudi Arabia Sunday of his "hopes for a peaceful vision of Islam" a day after Washington took issue with Shiite Iran.

Trump's major speech on Islam takes place on his first foreign trip as president and in the cradle of the Islamic faith.

It also comes a day after the United States and the Sunni Gulf kingdom signed agreements worth more than $380 billion -- almost a third of that military-related.

"That was a tremendous day. Tremendous investments in the United States," Trump said on Saturday at talks with Saudi King Salman.

"Hundreds of billions of dollars of investments into the United States and jobs, jobs, jobs."

His Secretary of State Rex Tillerson set the tone on Saturday when he urged Iran's newly re-elected President Hassan Rouhani to dismantle his country's "network of terrorism".

Tillerson also said the new arms deals signed between Riyadh and Washington aim to help Saudi Arabia deal "with malign Iranian influence".

Sunday's speech on Islam would be onerous for any US president, but for the real estate billionaire-turned-politician, it has the potential to be a high-risk exercise.

The speech has been touted as a major event along the lines of a landmark address to the Islamic world given by his predecessor Barack Obama in Cairo in 2009.

It will be especially sensitive given tensions sparked by the Trump administration's attempted travel ban targeting several Muslim-majority nations and accusations of anti-Islamic rhetoric while campaigning.

Trump's influential national security adviser, HR McMaster, has said he will deliver "an inspiring, direct speech".

"He will meet and have lunch with leaders of more than 50 Muslim countries, where he will deliver an inspiring, direct speech on the need to confront radical ideology and the president's hopes for a peaceful vision of Islam," McMaster said ahead of the visit.

He'll be very blunt

A White House official, speaking on condition of anonymity, said the speech would be "uplifting".

"He'll talk about what unites us in uplifting terms, but he'll also be very blunt in talking about the need to confront extremism and the fact that many in the Muslim world have not only not done enough, they've actively abetted this extremism, even as some of them have talked a good game on the surface but in quiet, continue to fund extremism."

In December 2015, Trump told a campaign rally he was calling for a "total shutdown" of Muslims entering the United States "until our country's representatives can figure out what the hell is going on".

His words shocked many Americans, with Trump detractors noting that the US Constitution prohibits religious discrimination.

"I think Islam hates us. There is a tremendous hatred there. We have to get to the bottom of it," Trump said in a March 2016 interview with CNN.

But now he is in the White House, Trump may chose a path not far removed from those of his predecessors, Obama and George W. Bush.

After Al-Qaeda claimed the 9/11 attacks on the United States, Bush visited a Washington mosque.

"Islam is peace," he said, insisting that "the face of terror is not the true faith of Islam".

And Obama chose Cairo University to deliver a speech detailing his vision of Islam in June 2009.

He addressed the world's 1.5 billion Muslims with the traditional Arabic greeting "Salam alaikum", and went on to call for "this cycle of suspicion and discord" to end.

Trump, who next travels to Israel and the Palestinian territories before visiting the Vatican, Brussels and Italy for NATO and G7 meetings, is looking to leave his domestic troubles behind.

James Comey, the former FBI chief fired by Trump, has agreed to testify publicly about Russian interference in the US elections.

Reports have also emerged that Trump called Comey "a nut job" and that the FBI have identified a senior White House official as a "significant person of interest" in its probe of Russian meddling.