LONDON • Foreign policy is about setting priorities between competing national interests. Seen from this perspective, it's clear what Western governments now need to do: their most urgent task is to destroy the so-called Islamic State in Iraq and Syria (ISIS) terrorist group which operates out of the Middle East, and that requires joining hands with Russia.

That is precisely what French President Francois Hollande advocated: Just days after terrorists in Paris killed 129 people and maimed hundreds more, he called for a formation of a "grand coalition" against terrorism. And that's also what Russian President Vladimir Putin appears to wish for: In his recent speeches, Mr Putin called for the creation of a global alliance "similar to the anti-Hitler coalition" of World War II, to fight "those who, just like the Nazis, sow evil and hatred of mankind".

Yet that's easier said than done. For despite a superficially similar stance against international terrorism, Russia's approach to the problem remains fundamentally different from that of Western governments. And far from helping to forge an alliance against terrorism, the history of Russian-Western cooperation which Mr Putin likes to recall is actually one of the biggest obstacles to cooperation. In short, neither the West nor the Russians are likely to bury their hatchets, notwithstanding the fact that they may have joint interests in the Middle East.

To some extent, the diplomatic showdown between Russia and the West, which started last year when Russian troops invaded Ukraine and annexed parts of that country's territory, is already being contained, with both sides toning down their hostile rhetoric. When Mr Putin attended the Group of 20 Brisbane summit of the world's biggest economies in Australia last year, he was shunned by most of the participants and left early for home, claiming he "needed sleep". But when Mr Putin recently attended this year's G-20 summit in Turkey, everyone sought his opinion; the enduring image of that summit was the photo of the Russian leader huddling with US President Barack Obama, earnestly discussing world affairs. So, Mr Putin, a former spy, has really come in from the cold.

Ironically, however, a mere week after that Putin-Obama encounter, relations between Turkey - the country which hosted the summit - and Russia nosedived, as the Turks shot down a Russian aircraft which violated their airspace. And talks about a joint Russian-Western approach to the war against ISIS in Syria also evaporated. Mr Hollande who jetted between Washington and Moscow in an attempt to forge an alliance "which will unify our strength and achieve a result that has been too long in coming", as he put it, had to admit that his efforts produced no results.

DIFFERENT AGENDAS

One obstacle preventing a deal is that Russia and the West have very different agendas in the Middle East. The United States and its European allies dominate the region; most of the regimes in the area are either pro-Western, or look up to the West for guidance and assistance. From the West's perspective, the defeat of ISIS and other terrorist organisations is the immediate objective, and the longer-term aim is to return the region to its previous status quo, as an area which enjoys some stability while continuing to act as the world's chief supplier of oil and gas.

But for Russia the main objective is to regain its previous role as a regional player in the Middle East, a position which the Soviet Union lost in the 1970s. The Russians would dearly like to see ISIS destroyed; after all, ISIS terrorists killed more Russian than French citizens when they blew up a Russian airliner carrying 224 passengers in early November.

But for Moscow, destroying ISIS is just a stepping stone to acquiring a broader strategic presence in the Middle East. Syrian President Bashar al-Assad is the only Arab leader Russia can count as an ally, and Moscow's first priority is to protect him; that's why Russian air strikes remain concentrated on opponents of the Syrian regime, rather than on ISIS hideouts in the country.

To suggest that "Russia must choose whether to save Assad or save the Syrian state", as Mr Obama publicly urged Mr Putin to do recently, is to put the cart before the horse: What Mr Putin wants first is a guarantee that Russia will be allowed to keep a foothold in the Middle East, and only then would he be prepared to abandon his support for the Assad regime.

Behind-the-scenes negotiations ironing out these difficulties are continuing in the Austrian capital of Vienna.

And Saudi Arabia may convene this week a conference of various rebel Syrian groups, in another effort to bridge the gap between the West and Russia.

Yet reaching a deal won't be easy. Many Western nations fear that Moscow's price won't be just an acknowledgment that Syria should be relegated to a Russian "sphere of influence", but also a Russian demand for the lifting of the Ukraine-related sanctions, and an acknowledgment that Ukraine will remain divided between Russian-controlled and Western-controlled areas.

This sort of "package deal" which ties an agreement with Syria to one on Ukraine is precisely what Mr Putin means with his constant references to the period of East-West cooperation during World War II; that war ended with a division into spheres of influence which Mr Putin wishes to replicate.

Some European leaders may consider such an arrangement acceptable: it will result in a concentration of massive firepower on Middle Eastern terrorists rather than constant bickering between Moscow and the West, and it will also put paid to dangerous security tensions in Europe. The only snag is that, even if a package deal of this sort can be concluded, it will achieve none of its desired objectives.

The former communist countries of central and Eastern Europe are guaranteed to oppose any accommodation with Russia over Ukraine, and have it within their powers to paralyse the European Union and Nato, the US-led military alliance in Europe, on this subject. That is the chief reason for the consensus in Europe that economic sanctions on Russia will be prolonged by six more months when they are up for renewal at the end of December; few believe sanctions serve any further purpose, but sanctions are the only policy the Europeans can agree on.

RUSSIAN POWER LIMITED

And even if, by some miracle, the Russians can be persuaded to cooperate on Syria while still being subjected to sanctions in Europe, it's difficult to see what Moscow can actually do in the Middle East. Like the West, the Russians don't want to put troops on the ground to fight the terrorists in Syria, and bombing ISIS from the air is no different from what the West is already doing; the last thing the anti-ISIS operations in the Middle East need now is extra air power.

The Russians may eventually be persuaded to sacrifice Mr Assad and replace him with a government of "national unity".

But they can't guarantee the survival of that government, nor can they guarantee that all of Syria's bewildering number of rebel groups would agree to lay down their weapons.

There is no question that Western governments should continue trying to reach an accommodation with Moscow, for Russia has it within its powers to complicate international conflicts, and to make their resolution more difficult. Cooperation with Russia is also required in order to avoid accidental clashes, such as the shooting down of the Russian jet by Turkey, a confrontation which could easily flare up again, with incalculable consequences.

But apart from a mischief-making capacity, Moscow does have the ability to influence conflicts in a more constructive way. Like the West, it suffers from an inability to deal with the phenomenon of terrorism in a coherent manner. And Russia's track record of combating religious extremism is even worse than that of Western governments.

So, no detente between the West and Russia is likely, nor relaxation in tensions. For what the Russians are offering by way of cooperation is not particularly exciting for Western nations, while the price Moscow is demanding for such cooperation remains far too high.