Turkey on Saturday dismissed US criticism that the Russian defence systems it has bought are not compatible with Ankara's NATO commitments.
The Pentagon on Friday strongly condemned the first test of a Russian-made S-400.
"We have been clear and unwavering in our position: an operational S-400 system is not consistent with Turkey's commitments as a US and NATO ally," said US Department of Defense spokesman Jonathan Hoffman.
But Turkey stood by its decision Saturday, insisting it was meeting its NATO commitments.
"Turkey's goal is not upset anyone but to ensure its people's security," defence ministry spokesperson Sebnem Aktop said in a statement.
The S-400 test came despite repeated warnings of sanctions from the US State Department if the system was activated.
President Recep Tayyip Erdogan on Friday confirmed the first test of the S-400 defence system saying: "We are not going to ask America for permission."
Aktop said the tests were part of "natural process" and made it clear they would use the S-400 system without integrating it into any NATO command control system -- following other alliance members who have S-300s.
Turkey has criticised the US for failing to sell it competing American Patriot missile defence batteries, arguing that it had to turn to Russia to address its security needs.