Turkey has received the first parts of a Russian S-400 missile defence system despite opposition from the US.
The shipment arrived in an airbase in the capital Ankara on Friday, the Turkish defence ministry says.
The move will anger the US, which has warned that Turkey cannot have both the S-400 anti-aircraft defence system and US F-35 fighter jets.
Turkey and the US are Nato allies – but Turkey has also been establishing closer links with Russia.
What’s the argument about?
Turkey has signed up to buying 100 US F-35 warplanes and has invested heavily in the F-35 programme. Turkish companies produce 937 of the plane’s parts.
But Turkey has also pursued an increasingly independent defence policy amid strained ties with the US and Europe. It has purchased Russia’s advanced S-400 air defence system for $2.5bn and sent members of its armed forces to Russia for training.
US defence officials said the S-400 is incompatible with the wider Nato air-defence system in the region.
The officials said they did not want the F-35 jets to be near S-400 systems because they feared Russian technicians would be able to access the F-35’s vulnerabilities.
The US warned that it would exclude Turkey from the F-35 programme if the S-400 deal went ahead, and warned that it could impose economic sanctions.
Turkey has argued that the two systems would be located in separate locations, and that the US was slow to offer an alternative missile defence shield.
President Recep Tayyip Erdogan said after a meeting with US President Donald Trump that he believes the US will not impose sanctions.