Former Nusra Front says US-led coalition struck HQ, killing 25

Planes reportedly belonging to the US-led coalition struck a local headquarters of the group formerly known as al-Nusra Front in Syria on Tuesday night, the group's spokesperson said.

Up to 25 members of Jabhat Fatah al-Sham, formerly known as the al-Qaeda affiliate al-Nusra Front, were killed when a building they were meeting in was struck in the northern province of Idlib.

The Syrian Observatory for Human Rights, a British-based monitor, said it was unclear who had carried out the attack.

Tuesday is the fifth day of a nationwide ceasefire in Syria but its sponsors, Russia and Turkey, say this excludes Islamic State and Jabhat Fateh al-Sham.

READ: Syrian army advances as rebel groups put peace talks on hold

Jabhat Fateh al-Sham spokesperson Abu Anas al-Shami, however, said the attack was carried out by the international coalition.

"The headquarters targeted by the international coalition a short time ago are a main headquarters for that area and contains a number branch offices, leading to the killing of the brothers," he said in a statement.

The Pentagon, which directs the US-led coalition's activities in Syria and Iraq, did not immediately comment on the statement.

It did confirm, however, that the US-led coalition had carried out flights in support of Turkish forces near the Islamic State-controlled Syrian town of al-Bab last week. However, it said it did not carry out air strikes, according to Pentagon spokesperson Peter Cook.

The flights were meant as a "visible show of force," Cook said on Tuesday.

"My understanding is that last week there was a request when some Turkish forces came under fire for air support and there... were flights conducted by the coalition at that time," Cook added.

The US-led coalition has been reluctant to provide support to NATO member Turkey in its advance towards al-Bab. Turkey recently called on the coalition to provide air support for Turkish-backed troops besieging the town, but its request was reportedly denied.

Russian fighter jets, however, last week bombed the town, aiding a Turkish advance on the ground.

Russian officials have insisted that the attack was not coordinated with Turkey.

Rebels supported by Turkish troops have laid siege to al-Bab for weeks under the "Euphrates Shield" operation launched by Turkey four months ago to sweep Islamic State militants and Kurdish fighters from areas close to its Syrian border.

A US defence official, speaking on the condition of anonymity, said the coalition's sorties took place on Thursday.