US Vice President Mike Pence once again warned Turkey on Wednesday against buying a Russian S-400 anti-missile system, Reuters reported.

“Turkey must choose. Does it want to remain a critical partner in the most successful military alliance in history or does it want to risk the security of that partnership by making such reckless decisions that undermine our alliance?” Pence said in remarks at a NATO event in Washington.

Earlier it was reported that Turkish FM Mevlyu Cavusoglu said that Turkey has proposed to the US  that they form a working group to determine that Russian S-400 missile defense systems do not pose a threat to U.S. or NATO military equipment.

“It will not be integrated into the NATO system ... therefore we propose the United States to establish a technical working group to make sure that this system will not be a threat - neither to (U.S.) F-35s nor the NATO systems,” Cavusoglu told a panel in the United States.