Saudi Arabia is preparing to spend millions of US dollars to arm and train thousands of Syrian fighters in a new national rebel force to help defeat Bashar al-Assad and act as a counterweight to increasingly powerful jihadist organisations.
Syrian, Arab and western sources say the intensifying Saudi effort is focused on Jaysh al-Islam - the Army of Islam, or JAI - which was created in September by a union of 43 Syrian groups. It is being billed as a new player on the fragmented rebel scene.
The force excludes al-Qaeda affiliates such as the Islamic State in Iraq and al-Sham and Jabhat al-Nusra, but embraces more non-jihadist Islamist and Salafi units.
According to one unconfirmed report, the JAI will be trained with Pakistani help, and estimates of its likely strength range from 5,000 to more than 50,000. But diplomats and experts warned on Thursday that there were serious doubts about its prospects as well as fears of "blowback" by extremists returning from Syria.
The Saudi intelligence chief, Prince Bandar bin Sultan, is also pressing the US to drop its objections to supplying anti-aircraft and anti-tank missiles to the JAI. Jordan is being urged to allow its territory to be used as a supply route into Syria. In return, diplomats say, Riyadh is encouraging the JAI to accept the authority of the US and western-backed Supreme Military Council, led by Salim Idriss, and the Syrian Opposition Coalition.
"There are two wars in Syria," said Mustafa Alani, an analyst for the Saudi-backed Gulf Research Centre. "One against the Syrian regime and one against al-Qaeda. Saudi Arabia is fighting both."
Saudi Arabia has long called publicly for arming the anti-Assad rebels and has bridled at US caution. It has been playing a more assertive role since September's US-Russian agreement on chemical weapons - which it saw as sparing the Syrian leader from US-led air strikes.
The JAI is led by Zahran Alloush, a Salafi and formerly head of Liwa al-Islam, one of the most effective rebel fighting forces in the Damascus area. Alloush recently held talks with Bandar along with Saudi businessmen who are financing individual rebel brigades under the JAI's banner. Other discreet co-ordinating meetings in Turkey have involved the Qatari foreign minister, Khaled al-Attiyeh, and the US envoy to Syria, Robert Ford.
It is too early, however, to see any impact of the Saudi move on the ground. "Militarily it's not significant," said one senior western official.
"I don't see it producing any dramatic change yet. It's a political step. These new rebel formations seem to be relabelling themselves and creating new leadership structures. It's part of a quite parochial political game - and above all a competition for resources."
Saudi assertiveness has grown along with unhappiness over US policy towards Syria and Iran, the kingdom's regional rival. Last month the Saudis cancelled their annual speech at the UN general assembly and turned down their first election to a security council seat in protest over the Syrian situation. The Saudis, like the Israelis, fear a US "grand bargain" that leaves Iran free to develop nuclear weapons.