ISTANBUL — As the Turkish government attempts to recalibrate relations with the new US administration under President Joe Biden, its acquisition of Russian-made S-400 missile defense systems remains a central point of contention between the longtime NATO allies.

Speaking in a press briefing Tuesday, Pentagon Press Secretary John F. Kirby urged Ankara to take action and remove the missiles from Turkish territory, reiterating a stance widely held by Washington officials that the S-400s pose a security threat to NATO defense systems in the country.

Shortly after acquiring the S-400s in July 2019, Turkey was removed from the bloc’s F-35 fighter jet program over concerns the missiles’ radars could collect data on the aircraft. Asked whether there were developments on the issue following a hint at a possible compromise by a Turkish official earlier this month, Kirby said there’s been no change in the Biden administration’s policy as Ankara reportedly pursues talks with Moscow over the purchase of a second batch of S-400 systems.

“We urge Turkey not to move ahead with the delivery of the S-400,” Kirby told reporters in Washington Tuesday. “We believe it's incompatible with the F-35, and Turkey remains suspended from that program. Again, we urge them not to retain it.”