The events of recent days in and around the Turkish town of Akcakale, close to Syria's northern border, serve as a warning of the extreme dangers inherent in the present situation. The sequence of events is now pretty well established. Shells fired by the Syrian military landed there on Wednesday afternoon, destroying buildings and killing five people. Turkey responded by firing into Syria. These were the first recorded cross-border incidents of Syria's civil war. The risk is that they will not be the last.

Turkey's parliament, called into emergency session, approved cross-border raids in the event of further incursions. Nato – of which, let it not be forgotten, Turkey is a full member – condemned Syria and warned against any repetition. The UN Security Council noted the "grave impact on regional peace and stability" in a statement that had been watered down by Russia.

The one positive conclusion to be drawn is that all parties seemed acutely aware of the perils and took steps to retreat from the brink. Thus Nato chose not to invoke Article 5, which states that an attack on one ally will be treated as an attack on all. Turkey did not insist upon it and Syria apologised for what it called "a tragic accident". The White House, keen to avoid anything that would intrude on next month's election, promised to support Turkey at the UN. The incident is thus effectively closed, until – it must be feared – the next time.

With violence raging in parts of Syria, cross-border clashes – either by mistake, as appeared to be the case this week, or deliberately, in pursuit of rebel fighters sheltering in Turkey – become ever harder to prevent. The UN has so far been unable or unwilling to halt Syria's descent into civil war. But the real risk now is that the conflict will spread, escalating into regional conflagration. Better late than never, this is the point at which Russia and China must make common cause with the other Big Five powers – or be culpable in what happens next.