Syria's government, amid growing tension between its ally Russian Federation and neighboring Turkey, is holding off on a planned offensive on a major rebel stronghold, giving Ankara more time to persuade armed groups to disperse.
The battle could bring an end to a seven-year-old uprising-turned-civil war, but at the cost of a humanitarian disaster on a scale yet unseen in the bloody conflict.
Officials estimate that almost 3 million civilians are in Idlib.
The reinforcements come during a lull in government and Russian bombings of rebel locations on Idlib's southern edge.
Idlib is located in the northwestern corner of Syria.
The lion's share of the rest is the Kurdish-controlled northeast.
The inquiry blamed the government for chlorine gas attacks during its offensive on eastern suburbs of the capital Damascus known as eastern Ghouta and on Idlib as well.
"More than 10,000 rebels in that province are believed to be aligned with Al-Qaeda".
The shipment entered the Turkey-backed al-Jabha al-Wataniya lil-Tahrir, or the National Front for Liberation, which was formed on August 1 from five rebel factions operating in Idlib and the northern countryside of Hama. With nowhere left to go, some might opt to fight till death rather than surrender.
But on Wednesday, the Observatory said the airstrikes that were targeting the rebels' positions had stopped and the military operation hasn't started.
Syrian government forces captured wide areas around the country from insurgents earlier this year.
During this process, the Western powers and Turkey have expressed dismay and rejection of such an offensive in Idlib, talking about a possible new influx of refugees to Turkey and Europe and the negative repercussion of a new wave of refugees, taking into consideration that foreign jihadists might infiltrate the ranks of civilians and reach Europe.
Turkey, which backs the anti-Assad opposition, has been warning Assad and his allies against attacking Idlib.
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There are also tens of thousands of rebels from Turkey-backed Free Syrian Army groups as well as millions of civilians - many already displaced from other parts of Syria.
"We will not act in the way the USA -led coalition acted in Mosul or in Raqqa when there were no negotiations about local cease-fires with opposition groups", he said.
Unprecedented levels of internal displacement took place in Syria this year, a United Nations commission said Wednesday.
Twice before, the USA has resorted to missile strikes in response to chemical weapons attacks, only to see them used again.
However last week Erdogan and Putin failed to agree on a ceasefire at a three-way summit in Tehran which also involved Iranian President Hassan Rouhani.
Speaking at a joint news conference with his Pakistani counterpart, Cavusoglu said Turkish President Tayyip Erdogan will speak with Russian President Vladimir Putin on the topic of Syria on Monday.
The U.N. envoy for Syria has told the U.N. Security Council there are signs the three leaders intend to continue talking.
Foreign Minister Mevlut Cavusoglu said Turkey had also contacted foreign ministers of several countries and was in touch with "all actors in Syria".
It warned that an attack on Idlib "with little regard for civilian life would generate a catastrophic human rights and humanitarian crisis". He said it would amount to "indiscriminate attacks to wipe out its opposition and not a genuine or effective campaign against terrorism".
An estimated 3mn people live in Idlib - the last major stronghold of active opposition to President Bashar al-Assad.
This is contrary to global humanitarian law, the OCHA spokesperson said, adding that one of the hospitals was also in a protected "deconfliction zone", whose coordinates had been given to the warring parties to spare it from attack. "We will continue our efforts with Iran and with Russian Federation".
Another tool in the US arsenal is economic pressure, but sanctions have been ineffectual since they first began to be applied during the Obama administration.