President Donald Trump on Tuesday hosted Saudi Crown Prince Mohammed bin Salman at the White House as the kingdom's de facto ruler seeks to reinforce his global standing following the 2018 killing of US-based journalist Jamal Khashoggi and deepen strategic ties with Washington.

In his opening remarks, Trump said Saudi Arabia has agreed to invest $600 billion in the US.

"That number could go up a little bit higher," The Guardian quoted him as saying. "But I don't know, we'll see," he added.