FILE PHOTO: Russian S-400 missile air defence systems are seen before the military parade to commemorate the 75th anniversary of the battle of Stalingrad in World War Two, in the city of Volgograd, Russia February 2, 2018. REUTERS/Tatyana Maleyeva

ISTANBUL (Reuters) - The planned delivery of Russian S-400 surface-to-air missile batteries to Turkey has been brought forward to July 2019, the Turkish undersecretary for defense industries said, from the first quarter of 2020.

Turkey and Russia signed the S-400 accord in December, finalizing a deal which deepened military ties between NATO member Turkey and the Kremlin.

The deal, reportedly worth some $2.5 billion, has worried the West because the system cannot be integrated into NATO’s military architecture.

“We brought forward the delivery date in the accord signed with Russia to provide the S-400 system and got a date of July 2019,” Turkish Undersecretary for Defence Industries Ismail Demir wrote on Twitter overnight.

His comment came after the two countries’ presidents held talks on Tuesday and marked the official start of work to build Turkey’s $20 billion first nuclear power station at Akkuyu on its Mediterranean coast.