The news from the Syrian city of Aleppo this weekend is bleaker than ever. The city’s long-suffering civilian population, having endured barrel bombs and toxic gas, find themselves in yet another terrifying situation. Those now injured cannot be evacuated and those trying to flee are running the gauntlet of Syrian troops and allied militias who evidence suggests have already shot dead women and children in cold blood.

Such extrajudicial executions would amount to war crimes, adding to a long list of documented violations of international humanitarian and human rights laws during this conflict. As our coverage today reveals, both Syrian government and rebel forces have blood on their hands in this respect.

Over the last few weeks there has been some considerable diplomatic self-flagellation over Aleppo’s plight. The simple, inescapable fact however is that the UN and the international community failed the people of Aleppo in their moment of need. Their suffering was not something that came out of the blue, but was a long, slow, torturous, process during which greater efforts could have been made to alleviate their pain.

Aleppo might now be facing its bloody endgame but across Syria some 39 communities remain under siege either by government forces and their allies or by rebel groups. This totals more than 1.3 million people who remain trapped and those surrounded by regime forces face a similar “surrender or starve” ultimatum by Assad’s forces, as did the people of Aleppo. This in itself is a grave breach of the Fourth Geneva Convention, and therefore a war crime.

These people more than ever need our help, and if nothing else what we have witnessed in Syria’s second largest city should motivate the international community to redouble its efforts to alleviate the suffering of others. This will be a task no easier than it was in Aleppo, but the moment of diplomatic hand wringing has long since passed, and the use of all political leverage possible must be brought to bear on the UN.

On another level too the UN and international rights bodies must take action. Again as our coverage today makes clear, already many Syrians and others are gathering the crucial evidence that could be used in bringing those who have committed war crimes to justice and punishment.

On this level at least those who have ordered the targetting of civilians or carried out torture, forced displacement, extrajudicial executions and other war crimes can later be brought to face international criminal courts in much the same way as the perpetrators of similar heinous acts were during the wars in the former Yugoslavia. The clear intention of doing that now needs to be set in stone. It might not stop the current killing but would focus the minds of those carrying out what are clearly crimes against humanity.