How the world twists, then turns!

Two years ago, a Turkish Air Force F-16 shot down a Russian Sukhoi SU-24M fighter it said had intruded some 2km into its airspace for less than 20 seconds.

On Monday, Turkish President Recep Tayyip Erdogan, with his Russian counterpart Vladimir Putin standing beside him, told the media that his country would buy the S-400 - Russia's most advanced long-range anti-missile system.

The deal is a Russian dagger in the heart of Nato, whose only Muslim-majority nation is Turkey. Nato's military chief has previously warned that Turkey, a Nato member for more than 50 years, might face restrictions on continued access to its mutual air defence system if it went through with the buy.

While the sale has been talked of for some months, it has special significance for the Muslim world, coming a week after United States President Donald Trump said he would move the American embassy from Tel Aviv to Jerusalem.

Turkey found its entry into the European Union denied after Germany called for an end to accession talks. Mr Erdogan, who has made some moves that could be perceived as flirting with fundamentalist Islam - the country is officially secular - is clearly making policy adjustments that now have moved into the strategic sphere. US Middle East policy has been increasingly clashing with Turkish interests.

For its part, Russia has been angered by Nato's eastward expansion and sees an opportunity to gain influence with a significant military power straddling the Middle East and Europe. This was why it quickly buried the hatchet with Ankara after the Sukhoi downing in November 2015.

Mr Putin's travels this week took him to Syria, where he announced a substantial reduction in Russian military presence after the defeat of the Islamic State in Iraq and Syria, and also to Egypt.

Russia thus far had sold the S-400 only to India, once a close ally, and China, with which it increasingly coordinates global policy.