President Donald Trump has claimed credit for saving “millions” of lives in Idlib, Syria despite only learning about the area recently, because he said he successfully halted a brutal regime offensive via a tweet.

Mr Trump said Wednesday he convinced Syria and its main allies, Russia and Iran, to hold off an anticipated attack on the northwestern province, home to 3 million people and one of the last rebel strongholds in the country.

Speaking on the sidelines of the United Nations General Assembly, Mr Trump explained that a message to his top team to “not let it happen” and a 4 September tweet, declaring Syria would be making a "grave humanitarian mistake”, saved the day.

However, he also admitted he had only recently heard about the province because a woman brought it up at a rally last month.

The US president said the woman had told him that Iranians, Russians and Syrians had surrounded Idlib and were going to “kill millions of people in order to get rid of 25,000 or 30,000 terrorists.”.

"I said that's not going to happen. I didn't hear of Idlib province. I came back and picked up the Failing New York Times and opened it up,” he continued.

“I said, 'Wow that's the same story the woman told me,' and I found hard to believe and I said how, why would anyone do that?"

Mr Trump said the story had indicated the offensive could start in the coming days and so he wrote his Twitter post. He gave orders to top officials, including Secretary of State Mike Pompeo and White House national security adviser John Bolton, to "not let it happen."

“Nobody is going to give me credit but that's OK because the people know,” Mr Trump added.

“I've had more Syrians thank me for that.”

A Syrian rebel fighter from the recently-formed 'National Liberation Front' takes part in combat training in Idlib province on 11 September (AFP/Getty Images)

Russia and Turkey, who back opposing sides of the seven-year civil war, agreed last week during a meeting in the Black Sea resort city of Sochi to set up a buffer zone in Idlib aimed at preventing a military assault.

The deal has so far staved off the anticipated offensive which the UN had warned could displace nearly a million people.

Mr Trump on Wednesday admitted that Iran, Russia and Syria deserved acknowledgement for not going through with the planned attack. He conceded that Turkey had also been "a big help."

Backed by Russian warplanes, the Syrian regime has largely corralled its opponents in Idlib after sweeping control of swathes of territory in Syria, through a combination of brutal offensives and evacuation deals.