BEIRUT (Reuters) - Air strikes killed at least 12 Islamist rebel fighters in Idlib province in northwestern Syria on Friday, the Syrian Observatory for Human Rights said.

Unidentified warplanes struck positions of the hardline jihadist Jund al-Aqsa group southeast of Idlib city, near the village of Sarmin, the British-based war monitoring group said.

It was unclear if those killed were from Jund al-Aqsa or other Islamist factions, it said, and they could have been fighters belonging to Hayat Tahrir al-Sham, an alliance of Islamist groups based in Idlib.

A Hayat Tahrir al-Sham media unit said the U.S.-led coalition hit one of its positions near Sarmin, killing six fighters.

Several Islamist factions, including al Qaeda’s former Syria branch, joined forces last week, calling themselves the Hayat Tahrir al-Sham (Liberation of the Levant Committee).

They said in a statement they had formed the alliance to mend splits among insurgent groups and strengthen opposition to the Syrian government.

A spate of U.S.-led coalition air strikes has targeted dozens of leaders and fighters of jihadist factions in Idlib over the past month, including from Jabhat Fateh al-Sham, the former al Qaeda-linked Nusra Front.