The attack caused the group, which had already lost its territory in Hama to al-Qaeda, to surrender.
"As a movement, the SRF is effectively finished," said Aymen al-Tammimi, a Syria analyst. "Nusra has driven them out of their strongholds of Idlib and Hama."
The collapse of the SRF and attacks on Harakat Hazm have dramatically weakened the presence of moderate rebel fighting groups in Syria, which, after almost four years of conflict is increasingly becoming a battle ground between the Syrian regime and jihadist organisations.
For the United States, the weapons they supplied falling into the hands of al-Qaeda is a realisation of a nightmare.
It was not immediately clear if American TOW missiles were among the stockpile surrendered to Jabhat al-Nusra on Saturday. However several Jabhat al-Nusra members on Twitter announced triumphantly that they were.
Also the loss of a group that had been held up to the international media as being exemplary of Western efforts in Syria is a humiliating blow at the time that the US is increasing its military involvement in the country, with both air strikes and training of local rebels.
In Idlib, Harakat Hazm gave up their positions to Jabhat al-Nusra "without firing a shot", according to some reports, and some of the men even defected to the jihadists.
In Aleppo, where Harakat Hazm also has a presence, the group has survived, but only by signing a ceasefire agreement with Jabhat al-Nusra, and giving up some of their checkpoints to the group.
Activists circulated the ceasefire document on social media last week.
Members of the al-Qaeda affiliated group Jabhat al-Nusra at a checkpoint in Aleppo, Syria
Jabhat al-Nusra reportedly attacked the groups in part because of personal skirmishes between units, in part because of its ambition to build an Islamic emirate that rivals that of Isil, and in part because they feared that the groups' closeness to the United States would pose a threat, analysts told The Telegraph.
Mr Tammimi said: "One of the conditions for giving Harakat Hazm weapons was that they did not work with Jabhat al-Nusra. The Western bolstering of these groups posed a threat to them."
The United States has been extremely cautious in how it supplies weapons to Syrian rebels in the civil war.
But it is this caution that has hampered the efforts of Syria's moderate rebels, and ultimately resulted in dominance of well-funded jihadist groups, analysts and local rebel commanders have said.
President Obama recent announced a new program, run by the US, Turkey and other allies to train and equip 5000 Syrian rebels to fight Isil.
But rigorous procedures to vet Syrian candidates for the programme mean it will be several months before military tuition can get under way, and up to one year before they have a force ready to fight the jihadists.
Last month one state department official said they would move "quickly" to initiate the program by sourcing men from groups the US already works with, including Harakat Hazm, but that it would still be three months before the programme got under way.
"We are sourcing men from brigades who we have already helped with logistical supplies. We have 16 groups so far, but that list is fluid and it can grow," the official said.
Now that process is likely to take even longer.
Meanwhile, a lack of weapons supplies have rendered moderate groups on the ground in Syria largely irrelevant.
Past efforts to build a fighting force on the ground who could fight the regime of President Bashar al-Assad collapsed in skirmishes between the rebels over the very limited weapons supplies.
The effort was also hampered by nations backing the opposition, including Saudi Arabia and Qatar, who would circumvent the military council established to supply arms and instead directly back the rebel groups they believed were most loyal to them, creating further divisions.
These efforts have since been revamped with new operations rooms in Turkey, to manage the north of Syria, and in Jordan, to manage rebel operations in the south including Deraa and Damascus suburbs. The operations rooms are manned by representatives from Turkey, the US, Britain, France, Saudi Arabia and the UAE, a Syrian source involved in the arms supplies told The Telegraph.
Qatar was reportedly thrown out over suggestions that it had been helping Jabhat al-Nusra, but is about to rejoin the effort.
"The operations rooms have been supplying anti-tank missiles, and individual GRAD rockets to rebel groups," the source said. "There are 11 groups that they are helping."
Rebel commanders apply for weapons directly to the operations rooms and state their case as to why they want the arms. "They have to apply for arms for individual missions," the source said.
The operations room member states then discuss the need and decide how many to give. "They never give more than six or seven anti-tank missiles in one go," the source said.
Then, if the commander wishes to continue to receive supplies, he has to return the used cartridges of the weapons to the operations room, thus proving that they used them and did not sell them on to another group.
The programme has given donor countries the confidence to arm the Syrian rebels, but it has created a "rubber stamp" system that is unwieldy, and too slow to keep up with the pace of the war in Syria and the needs of the men they are backing.
It has allowed better, privately, funded jihadist groups who focus less on fighting the Syrian regime than on taking control of territory already in opposition areas to grow in power.
And, in the face of infighting between rebel groups, and a weakened moderate opposition, the Syrian regime has continued to be able to bombard territory – including civilian neighbourhoods – with impunity.
Dozens of civilians were killed when regime planes bombed a refugee camp in Idlib last week.
It also means that any fighters trained by the United States and allies to fight Isil will be battling the jihadists whilst also contending with attacks by the Syrian regime.
"How can we successfully attack Isil, when the regime is bombing our rear bases and the homes of our families at our backs?" said one Syrian rebel about to be enrolled in the training.
Mr Tammimi said of the US-led efforts in Syria: "This attempt to cultivate groups includes such a thorough vetting process that it slows down the operation. Maybe it would have worked in the Syrian war 2012. Now it really is too little, too late."
Source : http://www.telegraph.co.uk/news/worldnews/middleeast/syria/11203825/Syrian-rebels-armed-and-trained-by-US-surrender-to-al-Qaeda.html