Turkey ignored US warnings as it continued Saturday to take delivery of Russia's S-400 missile defense system near Ankara, a defense ministry statement indicated.

"Delivery of S-400 Long Range Air and Missile Defense Systems resumed today," the statement said.

"The fourth Russian plane carrying S-400 parts landed at Murted Airport outside Ankara," it added.

The US fears that if Ankara integrates the S-400 into its defenses, data about the US-built F-35 fighter jet could leak back to the Russians, and Washington has threatened to deny Turkey access to the stealth aircraft.

The western defense alliance NATO, which counts Turkey as one of its members, is also "concerned about the potential consequences" of the S-400 purchase, an official told AFP.

Members of the US Congress have repeatedly voiced opposition to the move and threatened sanctions.

"President Erdogan was given a very clear choice. Unfortunately, he has clearly made the wrong one," said Eliot Engel and Michael McFaul, the top Democrat and Republican respectively on the House Foreign Affairs Committee.

Ankara rejects the US warnings, and on Friday, Foreign Minister Mevlut Cavusoglu told reporters: "We say this each time. This is a done deal. The process continues."

Turkey received the first batch of Russia's S-400 missile defense system on Friday. The Turkish defense ministry issued a statement confirming "the delivery of the first shipment of parts of the S-400 long range regional air missile defense system" had begun. 

Kremlin spokesperson Dmitry Peskov told journalists on Friday that "everything is happening in strict accordance with the agreements and signed contracts, all obligations are being carried out."

Washington has given Ankara until July 31 to cancel the S-400 purchase or have its pilots kicked off its F-35 training course and expelled from the US.

Trump's pick for Pentagon chief, Mark Esper, confronted the Turkish Defense Minister Hulusi Akar about the deal on the sidelines of a NATO meeting last month.