Turkish media broadcasts showed US-made F-16 fighter jets flying over Ankara Monday to test what appeared to be functioning Russian-made radars that are part of Turkey’s newly acquired S-400 missile defense systems.

The scene gave rise to speculation over whether the S-400s had been activated — a move that US officials have long threatened would trigger sanctions on Turkey. An unnamed Turkish defense official later confirmed the tests had taken place while speaking to Bloomberg News, and now Turkey observers expect lawmakers in Washington to punish Ankara for actions they say threaten NATO security systems.

The developments come less than two weeks after Turkish President Recep Tayyip Erdogan met with his American counterpart Donald Trump in the White House during an effort to ameliorate strained relations between the NATO allies. Though the two leaders have expressed an affinity for one another and Trump has so far shielded Ankara from repercussions following its S-400 purchase — as required under the Countering America’s Adversaries Through Sanctions Act (CAATSA) — members of Congress have introduced a multitude of sanctions packages that may soon be unleashed on Turkey.

Ozgur Unluhisarcikli, director of the German Marshall Fund in Ankara, said US sanctions on Turkey were “inevitable” after the radar tests.

Read more: al-monitor