The fourth Russian plane carrying S-400 parts reached the Mürted Air Base near capital Ankara early Saturday, the Defense Ministry said.

"The delivery of the S-400 Long Range Air and Missile Defense Systems are continuing today. The fourth Russian plane carrying S-400 parts landed at Mürted Airport outside Ankara," the ministry said on Twitter.

The first batch of S-400 parts started arriving Friday at Mürted Air Base, formerly called the Akıncı Air Base.

Turkey agreed in April 2017 to purchase the S-400 system from Russia following lengthy efforts to purchase an air defense system from the U.S. with no success.

U.S. officials have advised Turkey to buy the Patriot missile system rather than the S-400 system from Moscow, arguing it is incompatible with NATO systems.

Turkey has responded that it was the U.S.' refusal to sell it Patriots that led it to seek other sellers, adding Russia offered it a better deal, including technology transfers.