US President Donald Trump has accepted an offer to form a joint technical study group with Turkey to investigate Washington's concerns over Ankara's purchase of the Russian-made S-400 missile system, Middle East Eye has learned.

Axar.az reports citing foreign media that according to several Turkish officials, Trump, in a phone call with Turkish President Tayyip Erdogan on Wednesday, overruled the Pentagon and the State Department who had been against the study group.

US officials were concerned that Ankara's purchase of the missile system would put advanced stealth F-35 fighter jets, which Turkey has also ordered, at risk because Moscow could steal sensitive information through the system's radar.

Confident their assessment on the dangers posed by the missile system, US defence officials had refused to participate in the study group multiple times over the course of the past two months.

In a single phone call, that policy changed.

The White House and the US Defense Department did not return MEE's enquiries on the subject.