US Air Force planes. Photo: Wikimedia Commons.

The United States said it carried out a strike on Sunday against al Qaeda in northwest Syria, calling the area a “safe haven” for the group to plot attacks overseas.

The strike at a training facility targeted “operatives responsible for plotting external attacks threatening US citizens, our partners and innocent civilians,” US Central Command said in a statement.

The northwest is the last major territory in Syria still held by rebel groups fighting President Bashar al-Assad and is dominated by jihadist factions including Tahrir al-Sham, the latest iteration of al Qaeda’s former affiliate the Nusra Front.

The Syrian government is carrying out an offensive backed by Russian air power against the enclave that has caused hundreds of thousands of civilians, many already displaced, to flee their homes.

A US-led coalition has been fighting Islamic State in Syria since 2014 with an intensive air campaign and ground troops in support of local forces.

US forces have also carried out periodic strikes against suspected jihadist militants from al Qaeda and other groups elsewhere in Syria including in the northwest.