ANKARA, Turkey — Turkey’s government leaders are under increased pressure from the United States and other NATO allies not to unpack a Russian missile defense system for which the country paid $2.5 billion.

“It is not a correct approach to say ‘we won’t use them for their sake’ about a system that we bought out of necessity and paid so much money for,” said Ismail Demir, Turkey’s chief procurement official.

Despite U.S. threats of sanctions, Turkey plans to activate the S-400 air defense system in April, Demir said.

U.S. officials say Turkey should not unpack the system, which Russia delivered in July. Washington has expressed fear that system would put its operations at risk.

A U.S. diplomat in Ankara said the issue will be further negotiated between American and Turkish teams in the months ahead. “I am not sure if there will ever be a miracle solution,” he told Defense News, speaking on condition of anonymity. “From our point of view, the only solution is that the system remains unpacked.”

The diplomat also said it’s possible Russia could have remote access to the S-400 in Turkey and use a potential cyber backdoor to spy on NATO assets. “Planned data links that will come attached to S-400 batteries would be of questionable security due to growing Russian cyberwarfare capabilities. They could compromise not only NATO and U.S. assets on Turkish soil, but also NATO networks in general,” he said.

Turkey began receiving the S-400 system in July. It says delivery of a second batch of the S-400 system to the Turkish military may face delays next year due to ongoing negotiations with Russia over technology transfer and co-production options.

The negotiations combined with Western pressures complicates the situation in Turkey. “This has gone beyond a technical matter. It will require a decision from the top political authority,” a Turkish procurement official said. “We are hoping to find a point of conciliation.”

The U.S. is threatening to target Turkey with the Countering America’s Adversaries Through Sanctions Act — legislation that could place sanctions on Turkey if it begins operating S-400 batteries.

Turkish President Recep Tayyip Erdogan reiterated upon his return from a Nov. 13 visit to Washington that his government’s decision on the S-400 system is irrevocable.

In response to the S-400 purchase, the U.S. suspended Turkey’s partnership in the multinational Joint Strike Fighter program that builds the new generation F-35 Lightning II.