US forces on Saturday attacked jihadist leaders in northwestern Syria, the Pentagon said.
The strike left at least 40 dead.
It came at the same time as the Syrian regime renewed its attacks on the country's Idlib province, in a violation of the Russian-backed ceasefire which had reportedly gone into effect hours earlier, the Syrian Observatory for Human Rights said.
The US Department of Defense acknowledged an American attack, and said it had targeted Al-Qaeda leaders in northern Idlib. It did not, however, state which weapons were used.
In an emailed statement, the Central Command's Chief of Media Operations Lt. Col. Earl Brown said: "This operation targeted AQ-S leaders responsible for attacks threatening US citizens, our partners, and innocent civilians."
"Northwest Syria remains a safe haven where AQ-S leaders actively coordinate terrorist activities throughout the region and in the West. With our allies and partners, we will continue to target violent extremists to prevent them from using Syria as a safe haven.
"Additionally, the removal of this facility will further degrade their ability to conduct future attacks and destabilize the region."
He also emphasized that the destruction of the facility would further constrain Al-Qaeda’s ability to carry out attacks and destabilize the region.
CENTCOM declined to say what kind of weaponry was used, AFP added.
According to Observatory head Rami Abdel Rahman, the US attack "targeted a meeting held by the leaders of Hurras al-Deen, Ansar al-Tawhid and other allied groups inside a training camp" and killed 40.
Syrian's SANA on Saturday said the country's government agreed to the Idlib ceasefire, but quoted a Syrian military source who said the regime-backed forces "reserve the right to respond to violations" by jihadists and allied rebel groups.