Trump meets Syrian president before heading to Qatar

US President Donald Trump has met Syria's president in Saudi Arabia after a surprise US announcement it will lift all sanctions on the Islamist-led government, and says Washington is exploring the possibility of normalising ties with Damascus.

He made the comments on Wednesday during a summit between the United States and Gulf Arab countries.

Trump met Syria's Ahmed al-Sharaa before the summit.

Photos posted on Saudi state television showed them shaking hands in the presence of Saudi Arabia's crown prince.

Trump also urged Sharaa to normalise ties with Israel, a White House spokesperson said.

Despite concerns within sectors of his administration over Syria's leaders' former ties to al-Qaeda, Trump said on Tuesday during a speech in Riyadh he would lift sanctions on Syria in a major policy shift.

Turkish President Recep Tayyip Erdogan joined Trump and Saudi Crown Prince Mohammed bin Salman, also known as MbS, virtually in the meeting, Turkey's Anadolu News Agency reported.

MbS told the summit Saudi Arabia commended Trumps decision to lift sanctions on Syria.

The lifting of sanctions came despite deep Israeli suspicion of Sharaa's administration, worries initially shared by some US officials.

Israeli officials have continued to describe Sharaa as a jihadist, though he severed ties with al-Qaeda in 2016.

Israel's government did not immediately respond to requests for comment.

The decision is a major boost for Sharaa, who has been struggling to bring the country under the control of the Damascus government after toppling former president Bashar al-Assad in December.

The challenges were laid bare in March when Assad loyalists attacked government forces, prompting revenge attacks in which Islamist gunmen killed hundreds of civilians from the Alawite minority, drawing strong US condemnation.

Sharaa was for years the leader of al-Qaeda's official wing in the Syrian conflict. He first joined the group in Iraq, where he spent five years in a US prison.

The United States removed a $US10 million ($A15 million) bounty on Sharaa's head in December.

Trump's first day of a four-day swing through the Gulf region was marked by lavish ceremony and business deals, including a $US600 billion commitment from Saudi Arabia to invest in the US and $US142 billion in US arms sales to the kingdom.

Later on Wednesday, Trump will fly to the Qatari capital Doha, where he will take part in a state visit with Emir Sheikh Tamim bin Hamad al-Thani.

Qatar, a key US ally, is expected to announce hundreds of billions of dollars in investments in the US.

US ally Israel has opposed sanctions relief for Syria, but Trump on Tuesday said that Saudi's MbS and Erdogan, who are both close to the US president, encouraged him to make the move.

Trump's visit to Doha was to follow the White House's announcement this week that it plans to accept a Boeing 747-8 plane, which would be outfitted to serve as Air Force One, as a gift from the Qataris.

The luxury plane, which would be one of the most valuable gifts ever received by the US government, would eventually be donated to Trump's presidential library.

It has sparked outrage from Democrats and bipartisan security concerns, and some officials say it could create a perception of corruption.

Following his visit to Qatar, Trump will fly to Abu Dhabi to meet the UAE's leaders on Thursday.

He is then slated to fly back to Washington on Friday, but he has said he could fly to Turkey instead for a potential meeting between Russian President Vladimir Putin and Ukrainian President Volodymyr Zelenskiy.