Iraq has launched an air attack on a gathering of Islamic State leaders in Syria, killing 45 members of the hardline militant group, its military has said.

F-16 fighter jets destroyed three houses yesterday which were connected by a trench in the town of Hajin, where the leaders were meeting.

Those killed included high profile targets such as the group's "deputy war minister", one of its "media emirs", its leader Abu Bakr al-Baghdadi's personal courier and its chief of police, the military said in a statement.

The so-called Islamic State group, which once occupied a third of Iraq's territory, has been largely defeated in the country but still poses a threat along the border with Syria.

"Iraqi F-16 jets carried out a successful air strike that targeted a meeting of Daesh leaders ... in the Hajin area within Syrian territory. The operation resulted in the complete destruction of the targets, and the killing of around 45 terrorists," the military's Joint Operations Command said.

Daesh is an Arabic acronym for IS.

The Iraqi military has carried out several air strikes against IS in Syria since last year, with the approval of the Syrian government of President Bashar al-Assad and the US-led coalition fighting the militants.

Antonio Guterres called for "an immediate end to the current military escalation"

Meanwhile UN Secretary-General Antonio Guterres has called for an immediate end to a military escalation in southwest Syria and a return to ceasefire arrangements agreed by Russia, the US and Jordan.

US Ambassador Nikki Haley separately urged Russia to pressure its Syrian ally to uphold the truce.

Mr Guterres is scheduled to hold talks in Washington with Secretary of State Mike Pompeo later today.

Mr Assad has set his sights on retaking rebel-controlled parts of southern Syria.

Over the past three days, areas in eastern Daraa have been bombarded, forcing thousands of civilians to flee, according to the British-based Syrian Observatory for Human Rights.

Mr Guterres said he was "gravely concerned" by the recent upsurge in fighting from the Syrian government offensive, saying it posed "significant risks" to regional security.

He called for "an immediate end to the current military escalation" and urged all sides to uphold the ceasefire commitments "as a matter of priority."

Jordan, Russia and the US agreed last year to set up a de-escalation zone for the region that includes Daraa, Quneitra and Sweida. The area borders Jordan and the Golan Heights.

Ms Haley said in a statement earlier: "The Syrian regime's violations of the ceasefire in southwest Syria need to stop."

"We expect Russia to do its part to respect and enforce the ceasefire it helped establish, and to use the influence it has to stop the Syrian regime's violations and any further destabilising actions in the southwest and throughout Syria."

More than 11,000 people have been displaced in the upsurge of violence that has included air strikes, artillery, barrel bombs and rocket attacks, according to the US statement.

Assad's forces have retaken large parts of Syria from opposition fighters since Russia intervened militarily on its side in 2015.

The UN Security Council is scheduled to discuss Syria on Wednesday.