The rebels had almost reached the border when the hidden explosive device was set off; minutes later came bursts of intense firing. Four were killed immediately; around a dozen injured, some of them unlikely to survive because of the severity of their injuries. Three of the men were captured and, their comrades fear, may not be seen alive again.

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The target of the well-planned ambush by Bashar al-Assad’s forces was a group of 26 opposition representatives from Ghouta, the place where a few days earlier a chemical attack had killed more than a thousand people, a massacre which had led to one of the most serious international crisis in recent times with threats of US air strikes. What happened on 21 August in the Rif Dimashq governorate will be, the revolutionaries want to believe, the catalyst for foreign intervention with immense impact on the course of the vicious civil war. Ghouta now craves a key role in the crucial next stages of the conflict; less than 10 miles from the centre of Damascus, it would be the ideal strategic point for the rebels to strike at the fraying heart of the regime. Little wonder it became the target of Assad’s most vicious crime to date.

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After two and half years of increasingly savage strife, at a cost of more than 100,000 lives, many rebels hope the killings in Ghouta are the turning point; at last the US and its allies will take action. Even if the bombing does not take place, they expect a rapid escalation of support. If the West does not step in even now, they are certain the flow of arms from the Gulf will increase.

The seeming willingness of President Assad to hand over his chemical arsenal to international control is, they hold, a stalling tactic. However, if the stocks really are removed from the battlefield, with it will be removed the primeval fear such weapons have inspired among his opponents.

The Independent has spoken to people from Ghouta – some still living there, some in northern Syria in areas outside regime control and others in neighbouring Turkey – in an attempt to piece together the circumstances surrounding the chemical attack and also what the opposition on the ground want to see unfold in its aftermath.

The group of rebels killed last week were approaching the Jordanian border from Syria. They were a mixture of senior fighters and civilians on their way to meet foreign supporters of the Syrian opposition and members of its exiled leadership in Amman. There are, they claim, more than 40,000 fighters in Ghouta waiting for supplies and a co-ordinated plan to mount an assault on the capital.

The regime is fully aware of the grave danger on its doorstep and infuriated by the obdurate resistance it faces. The assault which had been going on for the last 10 months is continuing in Ghouta despite movements of its forces being restricted in other areas due to apprehension of American action.

“We are used to a hundred rockets and artillery [rounds] a day and that is still going on”, Abu Abdullah who has been trapped in the eastern part of the area for the last year was keen to stress. “We hear the Americans are going to be bombing, but the only bombing is being done by Bashar.”

An influential civic leader from Ghouta, using the name Mustapha Omar, maintained that the time of having to bear the constant pounding is coming to an end. He had arrived in Turkey from Jordan with a list of weapons needed to spring forward into the regime’s lair.

Mr Omar, a wealthy businessman, had spent a considerable amount of his own money equipping some of the khatibas (battalions) of rebel fighters in the area. He also helped facilitate the visit by UN inspectors to the sites of suspected chemical attacks in Ghouta by liaising with different groups of fighters. Mr Omar was now on a mission, in Jordan and Turkey, to obtain weapons from international backers. British officials have been among those he had been in contact with; they have not, he insisted, provided him with any arms. That is likely to come from sympathisers in the United Arab Emirates.

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“We are really after the UK’s help in training, but we may have to turn to the Americans, there is a lot going on in Jordan”, he said. Barack Obama announced last week that a first batch of 50 trained in the country by former US forces’ personnel were being sent into Syria.

“We are not saying that we in Ghouta are the best fighters, the toughest ones. But we are the ones the nearest to the capital, there is nowhere else that is such a good location to go to Assad and his people,” Mr Omar maintained. “Of course, Assad and his people know that. And that is the reason they had surrounded us for months, continually attacked us, used chemical weapons.” The Russian proposal on the regime’s chemical arsenal proves that “they have been using this poison. It’s a manoeuvre to avoid strikes, but it’s also a confession.”

Whether the regime used its chemical arsenal is, of course, at the centre of the raging accusations and recriminations and the view of Mr Omar and his side is, inevitably, highly partisan.

The US, Britain and France, among others, have charged the regime with deliberately attacking with sarin gas; it is the side with the military capability to do so. President Assad’s regime and its allies, chiefly Russia and Iran, have disputed that any weapon of mass destruction had been present .However, if it was used, then the responsibility for it, they claim, lies with the rebels.

Soon after the news of the deaths broke, a Russian foreign ministry spokesman stated that the nerve agent had been delivered by a home-made rocket fired from a rebel-held village. No evidence of this has been produced so far. Another account, widely circulated on the internet, is that Jabhat al-Nusra, a hardline Islamist group among the rebels, and foreign jihadists with them, were supplied with chemical components by Prince Bandar bin Sultan, the Saudi chief of intelligence, and stored in a tunnel where it was fatally mishandled.

Testimony from residents of Ghouta – not all of them supporters of the rebels – together with maps they provided, some of them hand-drawn, calls these scenarios into question. They repeatedly recounted separate landings of “chemicals” at Kafr Batna, Zayina, Ein Tarma, Zamalka, Ain Tarma and Moadamiyeh Al Sham, at varying times, pointing out that a single home-made rocket could not have carried out multiple strikes.

The Jabhat al-Nusra “own goal” explanation is also hotly disputed. The group, which has declared itself affiliated to al-Qa’ida, has grown in size and power in northern Syria, but it has no presence of any significance in Ghouta. The largest Islamist group in the area are the Liwa al-Islam, which the activists say are not as hardline as al-Nusra or the Islamic State in Iraq and al-Sham (Isis) – which is a branch of al-Qa’ida.

“Liwa al-Islam are not like al-Nusra, it is a different organisation, in a different area,” said Mr Omar. “We hardly have any foreign fighters in Ghouta. There is a Libyan I know, two or three from Saudi Arabia and a Jordanian. No Syrian rebel would use chemical weapons on their own communities; foreigners? But would the Saudis or anyone give such a big task to these few, no.”

Abu Abdullah was adamant: “Both east and west Ghouta are surrounded by the government. Do you think we would not know about some rebels bringing in chemical weapons? Do you think we would allow such things when we have our families, children there? Don’t we have enough problems with regime’s chemicals?”

The tunnels do exist and have been used to move about to avoid checkpoints, but any chemical accidents in them would not have reached the areas affected, the residents insisted.

Riadh Al-Nasri, a 23 year old medical student who was in eastern Ghouta on the night of the killings recalled: “There was a lot of shelling and rocketing, heavier than at many nights before, Moadmiyeh was particularly bad. We kept on hearing the word ‘chemical’ and people were suffocating. I went with friends to the field hospitals to help. We have seen lots of bodies, injured, dead, in this revolution. But these were different, there was no blood. When we were there they brought in more people, they were foaming at the mouth, through their noses, like children who have taken in soap.”

Sae’d, another medic, who was at Zamalka, said he was shocked: “The people brought in were vomiting, the pupils of their eyes were so small, they could not breathe, not just one or two, but dozens of them. I saw one whole row of people having muscle spasms, they had gone down to the cellars because they thought it was an ordinary bombing, neurotoxic agents fell through the air to them.”

Mr al-Nasri continued: “We had been to the field hospitals other times when they said they had chemical attacks, there have been people suffocating, not being able to speak, but nothing like this. Most of the people could not be saved, but we knew how important it was, it was decided that we must document everything very properly.”

He thought around 600 had died that night and morning, although “many more died because we did not have things like atrophine or biperiden”. Different opposition groups had put forward the number of fatalities between 350 to 1,729, the higher end making it the biggest loss of lives from a chemical attack since Saddam Hussein’s gassing of Kurds at Halabjah in 1988. The US Secretary of State, John Kerry, had repeatedly used a figure of 1,429, a precision which military and intelligence figures believe would have been impossible to pin down.

“Why does it matter, 500 or 5,000? You did not see what we saw, the mothers with dead babies, the mothers crying, the babies with their eyes just open,” Mr al-Nasri said angrily. “What about all the people killed by the regime using just bombs and their planes? Do we need to achieve a certain total of dead children before America, Britain does something?”

Mr Omar held that even without game-changing strikes, the regime will collapse soon. “We are seeing more and more soldiers coming over to us. Others are just running away, ministers are still defecting ” he stated. “Our friends need to back us so that this happens quickly. We want al-Ghouta to lead this not because we want revenge. It is to prevent revenge; we are not extremists. I know government officials who are technocrats who will be needed to rebuild the country; we don’t want to chop their heads off like some of the Islamists.”

Mr Omar and his colleagues feel that even with a rebel victory there has to be a negotiations. “We don’t want Assad to be killed the way Gaddafi was killed, we are not like that. We want him to face a court,” he said. “If that’s not possible he should leave the country with 100 of those closest to him. Look, some of us are still materially alright despite all that’s happened. What I say to the opposition who will form the next government is that when we negotiate to end this, we must not think of us, we must think of the mothers with poisoned babies in Ghouta.”