Turkish President Tayyip Erdogan confirmed on Friday that Turkey had been testing the Russian S-400 missile defence system and said US objections on the issue did not matter.
The US State Department last week condemned Nato ally Turkey over the test after repeated warnings over possible sanctions if the S-400 system was activated.
"It is true about the tests, they have been done and will continue," Mr Erdogan told reporters in Istanbul, confirming reports last Friday that the Turkish army conducted the test firing of the S-400s. "We're not going to ask America for permission."
Mr Erdogan stressed that the US opinion on the issue "did not bind" Turkey, adding: "If we're not going to test what we have in our hands, what else would we do?"
There had been hope in Washington that Ankara would "keep it in the box" but Turkey has always insisted the S-400s would be deployed after their delivery last year.
"We have also been clear on the potential serious consequences for our security relationship if Turkey activates the system," State Department spokeswoman Morgan Ortagus said last Friday.
Turkey faces US sanctions under a 2017 law known as CAATSA, which mandates sanctions for any "significant" purchases of weapons from Russia.
The two Nato allies have long been at odds over the S-400s. Turkey signed a deal to buy the systems from Russia in 2017 and deliveries of the first four missile batteries, worth $2.5 billion, began in July last year. Washington reacted by suspending Turkey from its F-35 jet programme.
Turkish officials have said the systems will not be integrated into Nato's defence infrastructure.
Ankara has accused Washington of failing to sell it the US-made Patriot missile defence system and said the purchase of the Russian system was to meet its security needs.
Mr Erdogan said Turkey would continue testing its military equipment including light, medium and heavy weapons, including many bought from the United States.
"It seems that the gentlemen [in the US] are especially bothered that this is a weapon belonging to Russia. We are determined, we are continuing on our path as always," he said.
The S-400 tests come at a particularly tense time in Turkey's relationships with Nato allies, the US, France and Germany, after Ankara resumed gas exploration this month in waters disputed by another alliance member, Greece.
Turkey has also been at odds with the US and France over its backing for Azerbaijan to retake the breakaway region of Nagorno-Karabakh by force, despite international efforts to end a flare-up in fighting that has claimed about 1,000 lives including civilians since September 27.