Turkey and Russia have signed an accord for Moscow to supply S-400 surface-to-air missile batteries, Turkish authorities have announced.
The deal, reportedly worth some $A3.5 billion, comes amid Turkey's strengthening ties with Russia and deteriorating relations with the United States and its other western countries.
Several allies are also concerned as the system cannot be integrated into NATO's existing military architecture.
NATO officials have warned Turkey about unspecified consequences of purchasing the S-400, but Turkish President Tayyip Erdogan claims ties with NATO remain strong.
And Ankara insists the systems would be used and managed "independently" by Turkish personnel, rather than Russian advisors.
Earlier on Friday, Turkish newspapers cited Erdogan as saying Turkey would borrow in the Russian currency in a loan deal under the accord.
"We will not borrow in dollars in this loan, we will borrow in roubles," Hurriyet newspaper quoted Erdogan on his return from a trip to Africa.
