US President Donald Trump welcomed Prime Minister Najib Razak to the White House on Tuesday, praising Malaysia for investments in the United States while steering clear of an American investigation into a major corruption scandal.

The visit is important for Najib, who faces elections in the coming months and wants to signal he is still welcome at the White House despite a criminal probe by the US Department of Justice (DOJ) into a state fund called 1MDB.

A senior US official acknowledged it was unusual to meet with Najib while 1MDB was under regulatory scrutiny.

"It's a weird situation, no doubt," the official said referring to the DOJ investigation, explaining that the administration has prioritised developing relations with Southeast Asian countries to counter "huge gains" China has made in the region during the past decade.

"There's a recognition under this administration that we can't continue to cede our relations in all these countries because of whatever the issue of the day is," the official said.

Flanked by top advisers in the Cabinet Room, Najib told Trump that Malaysia Airlines would buy 25 Boeing 737 jets and eight 787 Dreamliners, and would probably add another 25 737s in the near future – a deal he said would be worth more than US$10 billion within five years.

Najib said Malaysia's Employees Provident Fund, a major pension fund, wanted to spend US$3 billion to US$4 billion on US infrastructure development.

The White House had originally planned to allow reporters into an Oval Office meeting between Trump and Najib, but at the last minute changed course.

That meant photographers could not take the traditional photo of the two leaders sitting side by side, but a White House official said not to read anything into the change.

Najib had once enjoyed close ties with Trump's predecessor Barack Obama, playing golf with the Democratic president in Hawaii in 2014.

But relations cooled over concerns about human rights issues as well as the 1MDB scandal. Najib founded the fund, which is facing money laundering probes in at least six countries including the United States, Switzerland and Singapore. He has denied any wrongdoing.

The DOJ sued to seize some US$1.7 billion in assets it said were bought with misappropriated 1MDB funds.

The White House had said it would not comment on the DOJ investigation.

Trump praised Najib for his tough stand on Islamic State in Southeast Asia, and for cutting off economic ties with North Korea.

"He's been very, very strong on terrorism in Malaysia, and a great supporter from that standpoint," Trump said. "He does not do business with North Korea any longer, and we find that to be very important."

- Reuters

Don't mortgage our economy for Trump photo-op, Azmin tells Najib

Remarks by President Trump and Prime Minister Najib

White House: We didn't book Najib's stay at Trump Hotel

No press conference, Najib's media shy meeting with Trump

A lopsided meeting between Trump and Najib

Twitterjaya baffled by PM's pledge to 'strengthen' US economy

Critics using 1MDB to sabotage economy, Najib tells US-Asean businessmen

Trump likely to visit China during Asia trip

Meeting with Trump 'positive and friendly', says Najib

MAS to purchase 16 Boeing airplanes , MOU inked

Rosmah wants Permata Pintar students in grad school

Unusual for Najib, Trump to meet while 1MDB under probe, says US official