ANKARA -- Turkey on Saturday received second shipment of components of Russian S-400 air defense systems, the Defense Ministry said.

Local TV footage showed an Russian aircraft landing at Murted Air Base near the Turkish capital Ankara.

The Defense Ministry tweeted that the fourth Russian cargo plane carrying the missile system components arrived at the air base early Saturday.

The first shipment of S-400 air defense system parts started on Friday, with three huge Russian cargo planes arriving at the base, local media reported.

The third shipment "containing more than 120 guided missiles of various types" will be shipped by sea, according to Russia's state-run TASS news agency.

Turkey signed a contract with Russia in April 2017 to purchase the advanced S-400 systems. Tensions between the United States and Turkey have escalated in recent months over the deal.

Washington has repeatedly threatened to halt Turkey's purchase of F-35 fighters if Ankara goes ahead with the delivery of the S-400s.