US President Donald Trump vowed on Monday to do everything he can to make Syria successful after landmark talks with Syrian President Ahmed al-Sharaa, a former al Qaeda commander who until recently was sanctioned by Washington as a foreign terrorist.

Sharaa's visit capped a stunning year for the rebel-turned-ruler who toppled longtime autocratic leader Bashar al-Assad and has since travelled the world trying to depict himself as a moderate leader who wants to unify his war-ravaged nation and end its decades of international isolation.

One of Sharaa's chief aims in Washington was to push for full removal of the toughest US sanctions.

While he met with Trump behind closed doors, the US Treasury Department announced a 180-day extension of its suspension of enforcement of the so-called Caesar sanctions, but only the US Congress can lift them entirely.

Trump met with Sharaa in the first-ever visit by a Syrian president to Washington, six months after their first meeting in Saudi Arabia, where the US leader announced plans to lift sanctions, and just days after the US said he was no longer a "Specially Designated Global Terrorist."

In an unusually muted welcome, Sharaa, who once had a US$10 million bounty on his head set by Washington, arrived without the fanfare usually given to foreign dignitaries.

He entered through a side door where reporters only got a glimpse instead of through the West Wing main door where cameras often capture Trump greeting VIPs.

Speaking to reporters, Trump praised Sharaa as a "strong leader" and voiced confidence in him.

"We’ll do everything we can to make Syria successful," he said.

But Trump also gave a nod to Sharaa's controversial past. "We’ve all had rough pasts," he said.

Sharaa, 43, took power last year after his Islamist fighters launched a lightning offensive and overthrew longtime Syrian President Assad just days later on December 8.

Syria has since moved at a dizzying pace, away from Assad's key allies Iran and Russia and toward Turkey, the Gulf – and Washington.

Security was also expected to be a top focus of Sharaa's meeting with Trump, who in a major US policy shift has sought to help Syria's fragile transition.

Syria recently signed a political cooperation declaration with the US-led "Global Coalition to Defeat Islamic State," the Syrian information minister said in a post on X on Monday.

Just hours before the landmark talks, word emerged of two separate Islamic State plots to assassinate Sharaa that had been foiled over the last few months, according to a senior Syrian security official and a senior Middle Eastern official.

Over the weekend, the Syrian interior ministry launched a nationwide campaign targeting Islamic State cells across the country, arresting more than 70 suspects, government media said. (Reuters)