We can't let terrorists drive a wedge between potential allies in fight against them
If the carnage in Berlin's Christmas market and the murder of a leading Russian diplomat in Turkey have one common factor, it is that they demonstrate we are dealing with a new generation of terrorists who respect no boundaries when choosing their targets.
It has always been one of the central tenets of terrorist philosophy to identify targets that cause the maximum impact, both in terms of the numbers of civilians killed and maimed and the publicity the attacks generate.
But with this week's killings in Berlin and Ankara, they have added a new dimension to the terrorists' training manual, namely selecting targets that are guaranteed to sow discord among erstwhile allies, thereby weakening their resolve to tackle the terrorists by all means possible.
It is early days yet in the German authorities' investigation into the Berlin attack, with the police saying they are still hunting for the driver of a lorry that ploughed into a crowd of festive shoppers.
But the attack has piled further pressure on Chancellor Angela Merkel over her controversial policy to allow in an estimated million refugees of mainly Middle Eastern descent.
Nigel Farage, the former Ukip leader, will not be the only politician who believes, as he claimed in the aftermath of the attack, that Mrs Merkel must bear personal responsibility for the mass murder in the capital because of her refusal to back down on immigration.
She also faced stiff criticism from several prominent Eurosceptic German politicians, prompting fears that the attack will contribute to a further rise of populist political parties and groups, such as Alternative for Germany and Pegida (Patriotic Europeans Against the Islamisation of the West).
Any strengthening of their position prior to next summer's elections could lead to Mrs Merkel's defeat, an event that would not only deprive Europe of one of its most effective leaders, but would plunge the battered EU into even further chaos. Then the terrorists really will have succeeded in sowing discord and confusion throughout Europe.
The assassination of the Russian ambassador Andrei Karlov in the Turkish capital by a gunman said to have close links to Islamist groups fighting in Syria is an even more blatant attempt to drive a wedge between allies whose relationship is often defined more by their wariness of each other than political accord.
The rapprochement negotiated between Russia and Turkey under the auspices of senior Kazakh diplomats was primarily aimed at cooling the tensions that had arisen after the Turks shot down a Russian warplane that they claimed had violated Turkish airspace.
The incident in November last year occurred because the Russians and the Turks find themselves backing different sides in Syria's brutal civil war, with Moscow using its military might to prop up the regime of President Bashar al-Assad, while Turkish President Recep Tayyip Erdogan seeks the dictator's overthrow.
Indeed, the two sides, despite the recent diplomatic rapprochement, still remain committed to their opposing interests in the conflict.
There will undoubtedly be some Western policymakers who would like to see the terrorists responsible for Mr Karlov's murder succeed in their mission to end Turkey's diplomatic flirtation with Moscow, thereby causing Ankara to seek better relations with the West.
And it can certainly be argued that Turkey's long-term interests will be better protected by maintaining its long-standing ties with the West, especially through its membership of the Nato alliance, than by placing its fate in the hands of an opportunist like President Vladimir Putin, whose only interest seems to be furthering Moscow's territorial ambitions.
But, for the moment, the most pressing priority is to work out how best to tackle the Islamist terrorist networks that threaten the security of Russian and Turkish citizens, just as much as they do those living in the West.
So far as Europe is concerned, one priority must be to improve intelligence-sharing arrangements between countries to make sure terrorist cells are not able to act with impunity across international borders.
There were reports that material was circulating among the European intelligence community suggesting an attack on Berlin was imminent. If so, the authorities will want to know why it did not help to prevent the attack.
Another way to defeat the terrorists would be for Russia to co-operate with other world powers, rather than trying to undermine them through cyber attacks.
As the death of Mr Karlov demonstrates, the Russians are just as much a target of Islamist fanatics as anyone else who does not subscribe to their twisted ideology.