Britain and America's decision to suspend deliveries of non-lethal aid to Islamist rebels operating in northern Syria came after fighters from the Islamic Front drove the Western-backed Free Syrian Army (FSA) out of bases and warehouses contained American-supplied equipment in the north-western Syrian province of Idlib.

The significance of the British and American action is that it underlines their disillusionment with the Syrian rebels opposed to President Bashar al-Assad, whom they once lauded as the future rulers of Syria. Washington and London have been trying to target aid to groups opposed to the Islamic State of Iraq and the Levant (ISIL), the umbrella group for al-Qa'ida in Iraq and Syria, and the al-Nusra Front, another extreme jihadi Sunni military organisation.

In this case Britain and US are moving against the Islamic Front, an alliance of leading rebel groups including Ahrar al-Sham, Liwa al-Tawhid, Liwa al-Haq, Ansar al-Sham and the Kurdish Islamic Front, set up last month and with good relations with the al-Nusra Front. Its precise links to Saudi Arabia are unclear, but the Saudis have started to take a stronger leadership role in funding Syrian rebels since last summer, replacing Qatar which previously cooperated with Turkey in supporting the insurgency in Syria.

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Saudi willingness to spend seemingly limitless funds and the creation of the Islamic Front has inevitably weakened the FSA's Supreme Military Council and the Western-backed National Coalition, and is likely to increase fragmentation and extremism among rebels inside and outside Syria.

Louay Meqdad, a spokesperson for the FSA, said the move by the US and Britain was rushed and mistaken. “We hope our friends will rethink and wait for a few days when things will be clearer,” he said.

American intelligence officials estimate that there are 1,200 rebel military units ranging from groups based on extended families to those able to field several thousand fighters. Although opposed to ISIL, the Islamic Front is avowedly Sunni and sectarian in its orientation and opposed to a political solution of the civil war.

An important development in recent weeks in Syria has been the divergence between Saudi and American policy aims as a result of Saudi frustration that President Obama did not launch a military attack on Syria as after pro-Assad forces apparently used chemical weapons on a mass scale in Damascus on 21 August. In practice, this means that the Washington does not want to see Mr Assad replaced in the short term and one senior former US diplomat has called for confidential talks with the government in Damascus on combating al-Qa'ida linked groups.

Saudi impatience with US policy was further exacerbated by the interim deal last month between a US-led delegation and Iran on limiting Iran's nuclear programme. But it is doubtful if Saudi Arabia can truly adopt and stick with a separate policy from the US in Syria in which it funds a Sunni army 40,000 to 50,000 strong that is hostile to both al-Qa'ida linked movements and to Mr Assad. Belief that these groups are essentially warlords on the Saudi payroll is unlikely to increase their appeal to Syrian nationalists or to jihadis.

Saudi Arabia might be able to keep the war going in Syria but neither the rebels nor Mr Assad can win a decisive victory. The Syrian Army has recently succeeded in clearing the main Damascus to Homs road and are advancing on the town of Yabrud which is a notorious rebel strongpoint to the west of the main road in foothills of the Qalamoun Mountains.