The British-based Syrian Observatory for Human Rights reported more than 60 air raids in southern Idlib and the first responder group known as the White Helmets reported four civilian deaths in the village of Abdeen.
Idlib and nearby areas are largely controlled by Hayat Tahrir al-Sham, an alliance led by Al-Qaeda's former Syrian affiliate, as well as rival rebels.
Can the USA change the trajectory of a potential humanitarian catastrophe in Idlib?
With the Syrian Army continuing to amass troops and military hardware in southern Idlib, militants occupying the province are seemingly beginning to panic, warning Ankara against giving Damascus the greenlight to launch its long-awaited offensive in northwestern Syria. Many have previously refused to surrender to the regime. Beyond the risky prospect that the strikes could escalate the conflict (particularly given the Russian and Iranian presence in the country), they would also make it more hard for the United States and Russia to cooperate on a shared plan in Syria.
A possible regime attack on Syria's northwestern province of Idlib will sabotage the ongoing political process and cause a serious crisis of confidence, the Turkish presidential spokesman said on September 11.
Syria's last major rebel bastion Idlib was Saturday targeted by the "most violent" Russian air strikes in a month, a monitor said, after the failure of a three-way summit on the Syrian conflict.
About 3 million people live in the opposition-held area, which comprises most of Idlib province and adjacent small parts of Latakia, Hama and Aleppo provinces.
OCHA spokesman David Swanson told Reuters that as of Sunday, 30,542 people had been displaced from northwest Syria, moving to different areas across Idlib.More news: Trump rages over article on 'resistance' in White House
In an op-ed published in the Wall Street Journal on Monday, Turkish President Recep Tayyip Erdogan called on the global community to take action and said that an offensive on Idlib province would result in "serious humanitarian risks for Turkey, the rest of Europe and beyond".
The Assad regime has twice been targeted by USA air and missile strikes after previous alleged chemical attacks, and U.S. officials have in recent days said additional action would follow if Assad were to use the banned weapons in rebel-held Idlib.
Undersecretary-General for Humanitarian Affairs Mark Lowcock's comments in Geneva came days after Iran and Russian Federation backed a military campaign in the rebel-held area despite Turkey's pleas for a cease-fire.
"A major item on the summit's agenda was discussion of efforts to facilitate the return of Syrian refugees and internally displaced persons".
"The Astana process is ongoing, and with the help of the process we will have tangible results", he said, referring to the trilateral process with Iran and Turkey.
Many of Idlib's residents have already fled fighting in other areas of the country during Syria's seven-year civil war.
The attack, which came in response to what the United States and its allies insisted was another chemical attack in Douma, on the outskirts of Damascus, saw 105 cruise missiles being fired from sea and air at Syrian government targets.
On Friday, Turkish President Tayyip Erdogan said his country could no longer afford to take in any more refugees from Syria.