BEIRUT A powerful Syrian jihadist group has made rapid gains against more moderate factions in northern Hama and southern Idlib provinces in recent days, the Syrian Observatory for Human Rights monitoring group said on Friday.
Jund al-Aqsa, which has had links with the former al Qaeda branch in Syria, this week captured weapons and bases from groups operating under the Free Syrian Army (FSA) banner, and has detained dozens of rebel fighters, the Observatory said.
The advance of Jund al-Aqsa is another blow for foreign-backed rebel groups which have suffered defeats against Syrian government forces and been under attack by jihadist fighters in the west of the country in the last few months.
The largest intra-insurgent battle is taking place between FSA groups, which have joined forces with the powerful Islamist Ahrar al-Sham, and more hardline factions which have allied themselves to Jabhat Fateh al-Sham, the former al Qaeda branch.
Jund al-Aqsa's alliance in that particular battle, which is being fought in Idlib province, is not entirely clear.
It pledged allegiance to Fateh al-Sham, formerly the Nusra Front, in October.
But Fateh al-Sham rejected an "organisational allegiance" in a statement last month, citing disagreements within Jund al-Aqsa.
The Observatory said the advance by Jund al-Aqsa, which has been designated a terrorist organisation by the U.S. State Department, raised fears that the Syrian government and its Russian allies could use the presence of a jihadist group to wage fierce aerial assaults there.
Many more moderate rebel factions are party to a six-week-old shaky ceasefire between the government and the opposition. Jihadists such as Islamic State and al Qaeda linked fighters are not part of the truce.
(Reporting by John Davison; Editing by Robin Pomeroy)