UN Security Council Resolution 2249 pdf, passed on Nov 20, 2015, called on all Member States to "eradicate the safe haven they [ISIL all other individuals, groups, undertakings, and entities associated with Al-Qaida] have established over significant parts of Iraq and Syria":
“5. Calls upon Member States that have the capacity to do so to take all necessary measures, in compliance with international law, in particular with the United Nations Charter, as well as international human rights, refugee and humanitarian law, on the territory under the control of ISIL also known as Da’esh, in Syria and Iraq, to redouble and coordinate their efforts to prevent and suppress terrorist acts committed specifically by ISIL also known as Da’esh as well as ANF, and all other individuals, groups, undertakings, and entities associated with Al-Qaida, and other terrorist groups, as designated by the United Nations Security Council, and as may further be agreed by the International Syria Support Group (ISSG) and endorsed by the UN Security Council, pursuant to the statement of the International Syria Support Group (ISSG) of 14 November, and to eradicate the safe haven they have established over significant parts of Iraq and Syria;
On Dec 18, 2015, the UN Security Council passed follow-up [Resolution 2254](https://www.un.org/press/en/2015/sc12171.doc.htm Dec 18,2015), which re-iterated the call upon Member States to "to eradicate the safe haven" which AlQaeda and ISIS had "established over significant parts of Syria" and asserted, for complete certainty", "that the aforementioned ceasefire will not apply to offensive or defensive actions against" ISIS, AlQaeda and their allies"
"8. Reiterates its call in resolution 2249 (2015) for Member States to prevent and suppress terrorist acts committed specifically by Islamic State in Iraq and the Levant (ISIL, also known as Da’esh), Al-Nusra Front (ANF), and all other individuals, groups, undertakings, and entities associated with Al Qaeda or ISIL, and other terrorist groups, as designated by the Security Council, and as may further be agreed by the ISSG and determined by the Security Council, pursuant to the Statement of the ISSG of 14 November 2015, and to eradicate the safe haven they have established over significant parts of Syria, and notes that the aforementioned ceasefire will not apply to offensive or defensive actions against these individuals, groups, undertakings and entities, as set forth in the 14 November 2015 ISSG Statement;
In July 2017, Brett McGurk, the most senior US envoy to Syria and Iraq, stated that "Idlib Province is the largest AlQaeda safe haven since 9/11": NYT; Middle East Institute
Jenan Mousa reported in May 2017 that, out of 39 checkpoints in the three main roads in Idlib, 27 were held by Al-Nusra (one of the names of AlQaeda's Syrian faction) and close allies, 10 by Ahrar al-Sham, a Taliban-
Since then, AlQaeda consolidated its control by a swift attack on and defeat of Ahrar al-Sham, consolidating its control of Idlib even further, reported last year as follows:
The swift defeat of Ahrar al-Sham by its one-time ally Hay’at Tahrir al-Sham (HTS)[the current local name for AlQaeda's Syrian branch] was shocking to many people – Ahrar was, until that moment, considered one of the strongest Salafist factions in Syria. It had more manpower and, theoretically, more support, locally and regionally, than HTS. But in an offensive begun on 18 July [2017], HTS was quickly able to force Ahrar out of most of Idlib governorate as well as several other nearby regions.
The net result is that Idlib is not merely a "safe haven" for AlQaeda, but is being run and administered by AlQaeda, led by dedicated jihadists like Muhaysini:
With this consolidation of power in Idlib, according to Atlantic Council, it has become increasingly extremist:
the extremist trend among HTS has emerged in full force, which may just lead to the international community targeting it the way it now targets the Islamic State.
US Warnings
For reasons that remain inexplicable to me, the US has warned the Syrian government and Russia not to attack the AlQaeda safe haven in Idlib.
On Aug 31, Pompeo tweeted that an attack on AlQaeda's safe haven in Idlib would be an "escalation of already dangerous conflict":
Sergey Lavrov is defending Syrian and Russian assault on #Idlib. The Russians and Assad agreed not to permit this. The U.S sees this as an escalation of an already dangerous conflict.
On Sep 3, Trump warned that it would be a "grave" mistake for Syria to attack the AlQaeda safe haven in Idlib:
President Bashar al-Assad of Syria must not recklessly attack Idlib Province. 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!
Earlier today (Sep 6), Nikki Haley tweeted an even more threatening warning against an attack by Syria against the AlQaeda safe haven:
We want to take this opportunity to remind Assad and his Russian and Iranian partners: you don’t want to bet against the United States responding again.
The US has scheduled a meeting of the UN Security Council tomorrow in which it will presumably ratchet up US threats against Syria (and Russia) if it touches even a single hair of an AlQaeda beard in Idlib.