The first of the Russian S-400 air missile defense systems that Ankara has purchased will be loaded on to cargo planes on Sunday and are expected to arrive in Turkey sometime next week, Turkish Habertürk daily reported.

The initial S-400 delivery will be sent on two cargo planes from a Russian military air base, Habertürk said without citing a source. It also reported that a Russian technical team that would oversee its installation is expected to arrive in Turkey by Monday.

Tensions between the U.S. and Turkey have escalated in recent months over Ankara's purchase of S-400 systems, which Washington said will jeopardize Turkey's role in the F-35 fighter jet program and could trigger sanctions. During last week's G20 summit in Osaka, Japan, President Recep Tayyip Erdoğan said U.S. President Donald Trump told him there would be no sanctions against Turkey after it received the S-400 defense systems. At the summit, Trump blamed the standoff on then-President Barack Obama's refusal to sell Patriot missiles to Turkey, and said Turkey had not been treated fairly. Turkey decided in 2017 to purchase the S-400 system following protracted efforts to purchase air defense systems from the U.S. with no success. However, 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 the Patriots that led it to seek other sellers, adding that Russia offered a better deal, including technology transfers. Separately, Kremlin spokesman Dmitry Peskov said on Friday the S-400 air defense systems will be delivered as planned.