Saudi officials are preparing to pay the salaries of the Free Syria Army as a means of encouraging mass defections from the military and increasing pressure on the Assad regime, the Guardian has learned.

The move, which has been discussed between Riyadh and senior officials in the US and Arab world, is believed to be gaining momentum as a recent flush of weapons sent to rebel forces by Saudi Arabia and Qatar starts to make an impact on battlefields in Syria.

Officials in the Saudi capital embraced the idea when it was put to them by Arab officials in May, according to sources in three Arab states, around the same time that weapons started to flow across the southern Turkish border into the hands of Free Syria Army leaders.

Turkey has also allowed the establishment of a command centre in Istanbul which is co-ordinating supply lines in consultation with FSA leaders inside Syria. The centre is believed to be staffed by up to 22 people, most of them Syrian nationals.

The Guardian witnessed the transfer of weapons in early June near the Turkish frontier. Five men dressed in the style of Gulf Arabs arrived in a police station in the border village of Altima in Syria and finalised a transfer from the Turkish town of Reyhanli of around 50 boxes of rifles and ammunition, as well as a large shipment of medicines.

The men were treated with deference by local FSA leaders and were carrying large bundles of cash. They also received two prisoners held by rebels, who were allegedly members of the pro-regime militia, the Shabiha.

The influx of weapons has reinvigorated the insurrection in northern Syria, which less than six weeks ago was on the verge of being crushed.

The move to pay the guerrilla forces' salaries is seen as a chance to capitalise on the sense of renewed confidence, as well as provide a strong incentive for soldiers and officers to defect. The value of the Syrian pound has fallen sharply in value since the anti-regime revolt started 16 months ago, leading to a dramatic fall in purchasing power.

The plan centres on paying the FSA in either US dollars or euros, meaning their salaries would be restored to their pre-revolution levels, or possibly increased.

The US senator Joe Lieberman, who is actively supporting the Syrian opposition, discussed the issue of FSA salaries during a recent trip to Lebanon and Saudi Arabia.

His spokesman, Whitney Phillips, said: "Senator Lieberman has called for the US to provide robust and comprehensive support to the armed Syrian opposition, in co-ordination with our partners in the Middle East and Europe. He has specifically called for the US to work with our partners to provide the armed Syrian opposition with weapons, training, tactical intelligence, secure communications and other forms of support to change the military balance of power inside Syria.

"Senator Lieberman also supports the idea of ensuring that the armed opposition fighters receive regular and sufficient pay, although he does not believe it is necessary for the United States to provide this funding itself directly."

US defence secretary Leon Panetta said this week Washington was not playing a direct role in gun-running into northern Syria. "We made a decision not to provide lethal assistance at this point. I know others have made their own decisions."

Earlier this week the New York Times reported the CIA was operating in southern Turkey, helping allies decide which opposition fighters would get weapons.

Diplomatic sources have told the Guardian two US intelligence officers were in Syria's third city of Homs between December and early February, trying to establish command and control within rebel ranks.

Interviews with officials in three states reveal the influx of weapons – which includes kalashnikovs, rocket propelled grenades and anti-tank missiles – started in mid-May, when Saudi Arabia and Qatar finally moved on pledges they had made in February and March to arm rebel forces.

The officials, who insisted on anonymity, said the final agreement to move weapons from storage points inside Turkey into rebel hands was hard won, with Ankara first insisting on diplomatic cover from the Arab states and the US.

Turkey is understood to view the weapons supply lines as integral to the protection of its southern border, which is coming under increasing pressure as regime forces edge closer in an attempt to stop the gun-running and attack FSA units.

Turkey, Saudi Arabia and Qatar were all allies of Syrian leader Bashar al-Assad until several months into the uprising, which now poses a serious threat to his family's 42-year rule over the country.

All three states have become increasingly hostile as the revolt has continued, with Saudi Arabia in February describing the suggestion to arm rebel groups as an "excellent idea" and Qatar having offered exile to Assad and his family.

For the first few months of this year the three states were waiting for the US to take a proactive role in intervening in Syria, something Washington has so far not seriously considered.

With a presidential election later this year, and weighed down by the troubled legacy of Iraq, Barack Obama has shown no enthusiasm for a major foreign policy play. Polling in the US has consistently shown that voters have little appetite for intervention in Syria, while officials from Washington to London and Brussels have warned of grave risks to the region which may follow the fall of Damascus.

Assad continues to cast his regime's battle for survival as an existential threat from radical Sunni Islamists, who he says are backed by foreign states.

The Free Syria Army says its members are almost exclusively Syrian nationalists who disavow the world view of jihadists who flocked to neighbouring Iraq from 2004-07. It acknowledges that some foreign Arab fighters have travelled to Syria to join its ranks, particularly in Homs and in Douma near Damascus, but claims they do not play a decisive role.

Intelligence officials say a power vacuum would provide an attractive environment for militants who espouse a global jihad world view. "The next three to six months are crucial in Syria," one official said. "The ingredients are right for them [jihadists] to turn up and start acting decisively. That would not be a good outcome."