The delivery of the second battery of Russian S-400 missile defense systems has been completed according to the Turkish defense ministry.

:: Turkey’s defense ministry said on Sunday the delivery of the second battery of Russian S-400 missile defense systems has been completed, adding that the systems would become active in April 2020.

Ankara and Washington have been at loggerheads over Turkey’s purchase of the S-400 systems, which the US says are not compatible with NATO defenses and poses a threat to Lockheed Martin’s F-35 ‘stealth’ fighter jets.

The initial parts of the system were delivered to Ankara in July despite warnings about possible US sanctions over the purchase. The US has also expelled Turkey from the F-35 program, but Ankara has so far dismissed the warnings.

In a statement, the defense ministry said the delivery of the second S-400 battery to Ankara was completed. Efforts to mount the systems and train personnel who will use them were continuing, it said, adding that it planned to activate the S-400s in April 2020.

Turkish Foreign Minister Mevlut Cavusglu told an interview with CNN Turk on Saturday that the S-400s would be activated despite repeated US warnings.

“They (US officials) told us ‘don’t activate them and we can sort this out’, but we told them that we didn’t buy these systems as a prop,” Cavusoglu said, adding that Turkey would be open to buying US Raytheon Co Patriot systems as well.

In an interview on Friday, Turkish President Recep Tayyip Erdogan told Reuters he will discuss buying US Patriot missiles with US President Donald Trump this month, saying his personal bond with the US leader could overcome the crisis caused by the S-400s.

On Monday, US Treasury Secretary Steven Mnuchin said the Trump administration was considering imposing sanctions related to Turkey’s purchase of the S-400 systems, but no decisions have been made.

The dispute over the S-400 systems is one of several issues straining ties between the US and Turkey that include the ongoing conflict in Syria, among others.