This record is one of the deadliest inflicted on the jihadists in a single attack in this war-torn country.
"This operation targeted AQ-S leaders responsible for attacks threatening US citizens, our partners, as well as innocent civilians", the Pentagon said in a brief statement, without giving details of how the operation was conducted.
The Syrian Observatory for Human Rights (OSDH), which draws on a vast network of sources in Syria, said that missile fire had targeted a meeting gathering leaders jihadist groups Hourras al-Din and Ansar al-Tawhid and leaders of other extremist groups who are allied with them in a training camp.
"At least 40 of them"were killed, told AFP Rami Abdel Rahman, director of the OSDH.
The attack came on the first day of a truce in the bombardment of the Syrian regime and its Russian ally against the Idleb region.
The targeted groups are allies of the HTS, the former Syrian branch of Al Qaeda. All these factions have already been the target of air raids by the Syrian regime, its Russian ally, but also the international anti-jihadist coalition led by the United States, and the United States itself.
North of Idleb, successive explosions were heard, followed by columns of smoke, said an AFP correspondent present near the scene of the attack. Ambulances went on site while journalists did not have access.
On June 30, the United States struck a strike "against the leadership of Al Qaeda in Syria in a training structureIn the neighboring province of Aleppo, the OSDH claimed that the strike killed eight people, including six commanders of the group Hourras al-Din.
Truce diet Idleb
In 2014, the United States set up an international coalition to fight the Islamic State (IS) jihadist group, which was defeated last March in Syria with the help of Kurdish forces. But American soldiers are still there in Syria.
US strikes against jihadists have dropped significantly since 2017.
On another front of the war, the Syrian regime stopped its air strikes Saturday on the Idleb region, the first day of a truce announced after four months of devastating bombing, said the OSDH.
This truce was announced the day before by Russia, allied with the Syrian President of Bashar al-Assad that it helps in the conflict, particularly in its offensive against jihadists and rebels in the Idleb region, which has done more than 950 deaths among civilians since the end of April.
Ground fighting has also stopped, according to the NGO.
A previous truce decreed early August in this same region has shattered after a few days.
With the help of the cessation of hostilities, Ahmed Ibrahim returned home in the village of Maar Shourine near Maaret al-Noomane, time to recover some business.
"The regime, as usual, will violate the ceasefire and will not keep its promise", told AFP this Syrian who fled 15 days ago to a region further north.
In late April, the Assad Assisted Moscow regime launched air raids against Idleb Province and adjoining areas in the neighboring provinces of Hama, Latakia and Aleppo, dominated by HTS. On August 8, he began a ground offensive taking over many areas, including all the areas that escaped him in the province of Hama.
As a border country of Syria, Turkey has agreed with the United States to establish a buffer zone between the Turkish border and the areas of northeastern Syria controlled by Kurdish forces known as "terrorists"By Ankara On Saturday, Turkish President Recep Tayyip Erdogan threatened to launch a military operation in north-eastern Syria if his country did not get control of this"security zone".
The Assad regime recaptured about 60% of the territory with the help of Moscow, Iran and Lebanese Hezbollah. In addition to the region of Idleb, vast areas in the hands of Kurdish forces escape him.
Triggered in 2011 with the repression of pro-democracy protests, the war in Syria claimed more than 370,000 lives.