Rebels in southern Syria say they have taken a step towards unity that may attract more support from their Western and Arab backers, forging a joint defence pact to help shield them from government forces and Islamic State.
The south is the last major stronghold of the mainstream opposition to President Bashar al-Assad following the expansion of Islamic State in the east and north and gains by the al Qaeda-affiliated Nusra Front in the northwest.
A short drive from Damascus, the southern front remains a risk for Assad as he shores up his control over key areas of central Syria.
Insurgent groups including both mainstream rebels and Nusra have made slow but steady gains in the south against government forces, analysts who track the conflict say.
As the United States seeks partners on the ground for the campaign against Islamic State, the southern rebels are trying to address long-standing criticisms of the so-called moderate opposition by getting better organised.
"We are moving in steps. The joint defence agreement is part of the complete plan for uniting the southern front," said Bashar al-Zoubi, head of the Yarmouk Army - one of the biggest rebel groups in the south.
The agreement is dated December 6 and signed by 17 rebel leaders.
It follows an agreement among the southern groups on a transition plan for Syria.
With the war about to enter its fourth year, analysts say rivalries among a plethora non-jihadist groups have been one of their major weaknesses. The Turkey-based Syrian political opposition has little or no sway over the armed groups.
Rebels in the north last week unveiled a separate initiative grouping mainstream factions with hardline Islamists including Ahrar al-Sham - a group US Secretary of State John Kerry has equated with Islamic State.
That makes partnering with it a complicated prospect for Assad's Western opponents.