Turkey's purchase of Russian S-400s not an option but a 'necessity': minister

In a call between Turkish Defence Minister Hulusi Akar and his US counterpart, Akar said Turkey "remains under a serious air and missile threat" and that the purchase of S-400 systems was "not a choice but an obligation".

He also said Turkey was obliged to take measures against "intensive attacks" from the Syrian border as it is a priority for Ankara to protect its borders.

The call comes a day after Turkey received the first batch of Russia's S-400 missile defence system on Friday, sparking NATO "concern" and risking deepening tensions with the United States, which has repeatedly warned against the purchase.

A fourth Russian cargo plane delivered another shipment of the air defence equipment to Murted air base near Ankara on Saturday, Reuters reported.

Akar told US Defence Secretary Esper that Turkey's purchase of Russian S-400 missile systems does not mean a change in the country's strategic orientation, the Turkish defence ministry said in a statement.

The two men agreed a US delegation would visit Ankara next week to discuss the details.

NATO, which counts Turkey as one of its members, is "concerned about the potential consequences" of the purchase, an official told AFP. 

On Friday, Esper said Washington's stance had not changed.

The delivery is likely to escalate tensions with the US after Washington warned this week that there would be "real and negative" consequences if Ankara bought the Russian defence system. 

But Turkish President Recep Tayyip Erdogan said after meeting US counterpart Donald Trump last month that he was confident Ankara would not face sanctions for buying the Russian missile system.