UNITED NATIONS (Reuters) - U.S. President Donald Trump suggested on Wednesday he had never heard of the rebel-held Syrian region of Idlib under threat from Syrian government and Russian forces until a supporter brought it up at a recent rally about a month ago.

U.S. President Donald Trump addresses a news conference on the sidelines of the 73rd session of the United Nations General Assembly in New York, U.S., September 26, 2018. REUTERS/Carlos Barria

The United Nations says close to 3 million people live in the area, which also has thousands of Islamist fighters, and warned of a humanitarian catastrophe in the event of an offensive by government-backed forces that has been in the pipeline for several months.

A Russian-Turkish agreement last week staved off a threatened government attack by agreeing on the creation of a demilitarized zone between insurgent and government forces in the northwest.

Speaking at a news conference in New York, Trump took credit for convincing Russia, Iran and Syria to hold off on the attack after he warned them in a Sept. 4 Twitter post that they would be making a “grave humanitarian mistake to take part in this potential human tragedy.”

“Syria’s a mess and I was responsible (for stopping the offensive) and I hope it stays that way,” he said. “When I put out on social media a few weeks ago about Idlib province, I said, ‘Don’t do it’.”

Trump went on to explain that he had just learned about the situation in Idlib after a woman in the crowd at a rally brought it up.

“I was at a meeting with lots of supporters and a woman stood up and she said there is a province in Syria with 3 million people right now. The Iranians, Russians and Syrians are surrounding that province and they are going to kill my sister and 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 ... not the front page, but there was a very big story and 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?”

Trump said the story had indicated the offensive could start the next day and so he wrote his Twitter post and gave orders to his team, including Secretary of State Mike Pompeo and White House national security adviser John Bolton, to “not let it happen.”

“That doesn’t mean they can’t be selective, but don’t kill millions of people, and it stopped. Nobody is going to give me credit but that’s OK because the people know, but I’ve had more Syrians thank me for that. ... This was about four weeks ago I put that out,” Trump said.

Other Western leaders, including French President Emmanuel Macron, have also claimed that the coordinated public rhetoric calling on Syria and its allies to stop the offensive played a role in convincing them to back down.