US President Donald Trump began a meeting with Syria's president in Saudi Arabia on Wednesday after a surprise announcement that Washington would lift all sanctions on the Islamist-led government.

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.

Turkish President Recep Tayyip Erdogan took part via video conference in the meeting on Wednesday, Anadolu state news agency said.

Erdogan hailed Trump's decision to lift Syrian sanctions as one of historic importance, the agency said.

The US president's first day of a four-day swing through the Gulf region was marked by lavish ceremony and business deals, including a US$600 billion commitment from Saudi Arabia to invest in the United States and US$142 billion in arms sales to the kingdom.

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

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

US ally Israel has opposed sanctions relief for Syria, but Trump said on Tuesday that Saudi Crown Prince Mohammed bin Salman and Turkish President Tayyip Erdogan, who are both close to the US president, encouraged him to make the move.

His interactions with Sharaa, a former Al Qaeda commander who led rebel forces that toppled former Syrian president Bashar al-Assad in December, will be closely watched as observers gauge how serious Washington is about resetting its relationship with Damascus.

Sharaa renounced ties to al Qaeda in 2016.

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. Some officials have said it could create a perception of corruption, even absent a quid pro quo.

While the precise details of the investments Qatar plans to announce on Wednesday were unclear, Qatar Airways was expected to announce a deal to buy around 100 widebody jets from Boeing, according to a source.

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. (Reuters)