Withholding medical supplies is particularly vicious and shows the Syrian government's determination to reclaim Eastern Ghouta

Sieges are a merciless business, never more so than in Syria. As a UN aid convoy entered Eastern Ghouta, the World Health Organisation said that Syrian government security had forced the removal from its trucks of “all trauma kits, surgical, dialysis sessions and insulin”. Some 70 per cent of the medical supplies being sent were rejected according to a WHO official.

There is something disgustingly mean and vicious in targeting those who will die without dialysis or insulin. Depriving the sick of their last hope of life illuminates in the grimmest of ways how the siege of Eastern Ghouta, as in the other sieges that have been such a feature of the wars in Syria and Iraq, puts unbearable pressure on the weak and the vulnerable.

The aid convoy had already been cut back in size from food for a month for 70,000 to 27,500 people, though there is meant to be a second convoy in a few days. Even if this is not again depleted by government security forces, it is far too little for the 393,000 people estimated to be in this besieged eastern part of Damascus, though the chaos is such that nobody knows the true figure.

The siege is following much the same course as that of East Aleppo in 2016. The Syrian government is determined to retake the rebel-held zone by indiscriminate shelling and bombing combined with cutting off all supplies of food, fuel and medicine. It is making a ground assault that is crumbling the edges of the beleaguered enclave which is being systematically squeezed to death. The aim of the multiple assaults is to chop the area into smaller pieces that can be dealt with separately.

Sporadic aid convoys in such circumstances are really only a public relations ploy by the Syrian government and the Russians to ease the pressure of outraged international opinion. They do not affect the overall military course of the siege. Five years ago, President Bashar al-Assad held the centre of Damascus which was ringed – though they never quite linked up – by rebel-held districts that were isolated from the rest of the capital by checkpoints and were intermittently bombarded.

Almost all these opposition enclaves have been forced to surrender and the only sizeable one still holding out has been Eastern Ghouta. After 2013 it was loosely blockaded, but access was fairly easy through one main entry and exit point and an elaborate system of tunnels. Both of these were closed in 2017 and the blockade turned into a regular siege conducted very much on the medieval principles of starving and battering those surrounded into submission.

The main weapon in all cases is air strikes and artillery because armies know that the only alternative is a ground assault and street fighting in which the attackers will suffer heavy losses. This is as true of the US-led coalition’s assault on Mosul in Iraq and Raqqa in Syria last year as it is of the Syrian government and Russian assault on East Aleppo and Eastern Ghouta. The US-led air war is supposedly more humane and directed solely at military targets. But I was in Raqqa last Sunday and the overwhelming impression is of universal destruction similar to that of the carpet bombed German cities in the Second World War.

Proof of this is emerging. A detailed study of 150 air strikes by The New York Times last year revealed that, while the US air force claimed that one in 157 of its air strikes led to civilian deaths, the real figure was probably one in five. In the Qaiyara district south of Mosul, the US said its aircraft had killed one civilian, but the real figure was 43 dead, 24 of them women and children. Casualties in the Old City of Mosul were devastating because air strikes were focused on a smaller and smaller area as Isis shot anybody who tried to escape.

What should now be done to limit civilian casualties in Eastern Ghouta? As in East Aleppo, the enclave’s fall is inevitable and anything that prolongs the battle there will only lead to more dead and disabled. Humanitarian corridors are needed, but these are not much good without UN monitors ensuring the ceasefire is real. Most of the discussion is about what should happen to the civilians, but the outcome of these sieges is invariably determined negotiations between the besiegers and the armed opposition defenders, who, in the case of Eastern Ghouta, are said to number 10,000 fighters. In past sieges, these have been given the choice of an amnesty of some description or evacuation with light weapons to a rebel stronghold, almost invariably Idlib in the north-west of Syria.

None of these past prescriptions quite fit Eastern Ghouta because of its size and because rebel fighters like the Army of Islam, which controls Douma, the largest population centre under attack, do not have another base to which they can go. But even the most successful evacuations are stories of misery and terror which will continue so long as the war in Syria goes on.

Where foreign powers could do most good is by preventing such sieges starting in the first place. Once besieger and besieged are locked in unequal combat there is little the outside world can do about it, aside from a general wringing of hands.

It so happens that the makings of another Eastern Ghouta is under way in northern Syria, though with little of the publicity given to the situation in Damascus. The Turkish army and its Arab militia allies are surrounding the Kurdish enclave of Afrin, which has much the same population as Eastern Ghouta. A few days ago Turkish shelling and bombing had killed 204 civilians, 61 of them children according to authorities in Afrin.

The Kurds say they will fight to the end and quite certainly mean it. The only outlet from Afrin not held by the Turks or their allies is through a road held by the Syrian government which might be closed at any time. The impending siege of Afrin is likely to be as bad in terms of human suffering as anything we have seen in the Syrian Civil War but, unlike Eastern Ghouta, there may still be time to avert it.