Vaciha Turki Al Omar, 30, has been in Idlib for seven months. She on the hill overlooking the sprawling refugee camp with her kids. "We can try to fight but the kids are our weakness so we must run away," she says.
PHOTO: Gul Tuysuz
Vaciha Turki Al Omar, 30, has been in Idlib for seven months. She on the hill overlooking the sprawling refugee camp with her kids. "We can try to fight but the kids are our weakness so we must run away," she says.
Now playing
03:54
Major rebel stronghold in Syria under threat
President Donald Trump addresses the 73rd session of the United Nations General Assembly, at U.N. headquarters, Tuesday, Sept. 25, 2018. (AP Photo/Richard Drew)
PHOTO: Richard Drew/AP
President Donald Trump addresses the 73rd session of the United Nations General Assembly, at U.N. headquarters, Tuesday, Sept. 25, 2018. (AP Photo/Richard Drew)
Now playing
02:17
Trump claim to world leaders met with laughter
Trump laughing with me
PHOTO: CNN
Trump laughing with me
Now playing
01:38
Trump: World leaders were laughing with me
PHOTO: CNN Illustration/Getty Images
Now playing
01:59
Trump warns about doing business with Iran
President Donald Trump talks on the phone aboard Air Force One during a flight to Philadelphia, Pennsylvania, to address a joint gathering of House and Senate Republicans, Thursday, January 26, 2017. This was the Presidentâs first Trip aboard Air Force One. (Official White House Photo by Shealah Craighead)
PHOTO: Shealah Craighead/White House Photo/Getty Images
President Donald Trump talks on the phone aboard Air Force One during a flight to Philadelphia, Pennsylvania, to address a joint gathering of House and Senate Republicans, Thursday, January 26, 2017. This was the Presidentâs first Trip aboard Air Force One. (Official White House Photo by Shealah Craighead)
Now playing
01:36
WH stops summarizing calls with world leaders
PHOTO: CNN
Now playing
01:32
Clarke: Trump diminishes US role and influence
US President Donald Trump and Russia
PHOTO: BRENDAN SMIALOWSKI/AFP/Getty Images
US President Donald Trump and Russia's President Vladimir Putin attend a joint press conference after a meeting at the Presidential Palace in Helsinki, on July 16, 2018. (Photo by Brendan SMIALOWSKI / AFP) (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
Now playing
01:59
Trump: We are all to blame for Russia relations
SAN FRANCISCO, CA - FEBRUARY 08:  Canada Prime Minister Justin Trudeau looks on before speaking to members of the media during a visit to AppDirect on February 8, 2018 in San Francisco, California. Trudeau is visiting several cities in the U.S.  (Photo by Justin Sullivan/Getty Images)
PHOTO: Justin Sullivan/Getty Images North America/Getty Images
SAN FRANCISCO, CA - FEBRUARY 08: Canada Prime Minister Justin Trudeau looks on before speaking to members of the media during a visit to AppDirect on February 8, 2018 in San Francisco, California. Trudeau is visiting several cities in the U.S. (Photo by Justin Sullivan/Getty Images)
Now playing
00:57
WaPo: Trump admits he gave Trudeau false info
US President Donald Trump and French President Emmanuel Macron hold a joint press conference at the White House in Washington, DC, on April 24, 2018. (Photo by LUDOVIC MARIN / AFP)        (Photo credit should read LUDOVIC MARIN/AFP/Getty Images)
PHOTO: LUDOVIC MARIN/AFP/Getty Images
US President Donald Trump and French President Emmanuel Macron hold a joint press conference at the White House in Washington, DC, on April 24, 2018. (Photo by LUDOVIC MARIN / AFP) (Photo credit should read LUDOVIC MARIN/AFP/Getty Images)
Now playing
00:44
Trump has 'terrible' phone call with Macron
PHOTO: photo illustration: getty images/shutterstock/cnnmoney
Now playing
01:17
WH confirms Trump, Putin discussed meeting
travel ban trump then and now orig nws_00002328.jpg
travel ban trump then and now orig nws_00002328.jpg
Now playing
01:23
Trump's travel ban then and now
PHOTO: ABC News
Now playing
01:01
Trump touts trust with Kim in TV interview
PHOTO: Kevin Lim/THE STRAITS TIMES
Now playing
02:11
Memorable moments from the Singapore summit
TOPSHOT - A vendor picks up a 100 yuan note above a newspaper featuring a photo of US president-elect Donald Trump, at a news stand in Beijing on November 10, 2016.
The world
PHOTO: GREG BAKER/AFP/AFP/Getty Images
TOPSHOT - A vendor picks up a 100 yuan note above a newspaper featuring a photo of US president-elect Donald Trump, at a news stand in Beijing on November 10, 2016. The world's second-largest economy is US president-elect Donald Trump's designated bogeyman, threatening it on the campaign trail with tariffs for stealing American jobs, but analysts say US protectionism could create opportunities for Beijing. / AFP / GREG BAKER (Photo credit should read GREG BAKER/AFP/Getty Images)
Now playing
01:48
US trade with China, explained
PHOTO: CNN
Now playing
01:07
Trump announces withdrawal from Iran deal
US President Donald J. Trump delivers his first address to a joint session of Congress from the floor of the House of Representatives in Washington, DC, USA, 28 February 2017.   / AFP / EPA POOL / JIM LO SCALZO        (Photo credit should read JIM LO SCALZO/AFP/Getty Images)
PHOTO: JIM LO SCALZO/AFP/Getty Images
US President Donald J. Trump delivers his first address to a joint session of Congress from the floor of the House of Representatives in Washington, DC, USA, 28 February 2017. / AFP / EPA POOL / JIM LO SCALZO (Photo credit should read JIM LO SCALZO/AFP/Getty Images)
Now playing
01:46
Trump's foreign policy: One thing to know
(CNN) —  

President Donald Trump warned Syria and its allies Russia and Iran on Monday against attacking the last major rebel stronghold of Idlib province in the country’s northwest.

“President Bashar al-Assad of Syria must not recklessly attack Idlib Province,” Trump wrote on Twitter. “The Russians and Iranians would be making a grave humanitarian mistake to take part in this potential human tragedy. Hundreds of thousands of people could be killed. Don’t let that happen!”

Hours after the tweet, Russian planes struck parts of western Idlib, according to an activist media group and Syrian rescue group the White Helmets. The White Helmets said rescues were underway amid “intensive airstrikes.”

The President’s warning comes just days after Secretary of State Mike Pompeo issued a similar warning to Russia’s foreign minister, Sergey Lavrov, saying an attack on Idlib was something that Syria and Russia “agreed not to permit,” and that the US “sees this as an escalation of an already dangerous conflict.”

US officials have grown worried that an assault on Idlib could involve the use of chemical weapons if the rebels are able to slow regime advances.

Syrian President Assad’s regime has moved armed helicopters closer to Idlib in recent weeks, according to two defense officials. The US is concerned they could eventually be used to launch another chemical attack as well as a conventional assault.

The day before Pompeo’s warning, Lavrov told Western nations not to “play with fire” over Idlib and claimed the White Helmets, a group of unarmed volunteer rescue workers, were preparing to stage a chemical strike to blame on the Syrian government as a pretext for military action.

The Pentagon responded Friday, saying, “Russia has recently launched a concentrated disinformation campaign to discredit the United States and international partners and allies” and calling Lavrov’s allegation about preparations for a staged chemical strike “absurd.”

CNN reported Friday that US intelligence and military targeting experts have created a list of Syrian chemical weapons facilities that could be struck if Trump decided to order a new round of airstrikes in the country.

So far, a decision to take action has not been made, but one administration official with direct knowledge of the situation told CNN the military “could respond very quickly” if Syria launched a chemical weapons attack.

Iranian Foreign Minister Javad Zarif arrived in Damascus on Monday, and told reporters he hoped that events in Idlib went the same as operations in the past.

“We hope that the province of Idlib will be cleared of terrorism the same way as with previous operations of the Syrian military, with the lowest casualties, such as the suburbs of Damascus and the southern provinces,” Zarif said.

Earlier this year, weeks of violence displaced 320,000 people in the southern province of Daraa, after the Russian-backed Syrian military launched an offensive to recapture the town.

Eventually the rebels came to a reconciliation agreement with the Syrian government in which the fighters agreed to hand over their weapons to Syrian forces. Anyone who didn’t want to be part of the agreement was to have been allowed to transfer to Idlib.

About 6.2 million Syrians have been displaced since the conflict began in 2011, with a further 6.3 million having fled abroad as refugees, according to a recent UNHCR report.

’Humanitarian catastrophe’

Idlib is home to some 3 million Syrians, according to United Nations estimates, and 70,000 fighters from multiple factions, including former al Qaeda affiliate Hayat Tahrir al-Sham. The heavy concentration of residents and fighters, analysts say, makes the province a powder keg.

“Idlib would see a humanitarian catastrophe that exceeds the level of any seen in the Syrian conflict so far,” said Lina Khatib, head of the Middle East and North Africa program at the Chatham House think tank in London.

“You have the potential for civilians to be not just targeted by the regime but also to be caught in battles through which these rebel groups aim to defend against regime attacks,” said Khatib.

Half of Idlib’s population are displaced people, bused to the northwestern province from former rebel areas across the country. The area is densely populated, with many civilians flocking to camps near Syria’s border with Turkey as they brace for an imminent attack.

Turkey, which has closed its border to fighters and civilians, has vowed that a regime incursion into Idlib would constitute a “red line.” But analysts say there is little that it can do in the face of Russian and Syrian resolve to root out the fighters.

“There’s a lot of tough jihadists in the region and Syria’s not going to digest them. The regime is not going to accept them, so they’ve got their backs against the wall,” said Joshua Landis, director of Middle East Studies at the University of Oklahoma.

“They’re facing death, and Turkey has made it clear that they’re not going to take them.”

Idlib hosts a ragtag group of rebels, including Chechen and Chinese Uyghur fighters. In 2017, Brett McGurk, the special presidential envoy for the global coalition against ISIS, called Idlib province “the largest al Qaeda safe haven since 9/11.”

“There’s no good solution to this. It’s a very raggedy ending to a horrible war which has had nothing but tragedy,” said Landis.

CNN’s Barbara Starr contributed to this report.