The drama over a North Carolina pastor detained in Turkey showed no signs of abating as Turkish President Recep Tayyip Erdogan vowed to not bow before the threat of US sanctions over the affair. With both sides refusing to de-escalate, salvaging battered relations between the two NATO allies will be harder than ever.

“You cannot force Turkey to cave to sanctions,” Erdogan told reporters in Zambia before heading home, warning, “If the [United States] does not change this attitude, they should not forget they will lose a sincere and strong partner like Turkey.” Erdogan added Turkey had “other alternatives” and noted that Iran had not collapsed when it was slapped with US sanctions.

The Turkish leader was responding to last week’s unexpected salvoes from President Donald Trump and Vice President Mike Pence over the plight of Andrew Brunson, who is being held on what US officials call bogus espionage and terrorism charges. Trump took to Twitter on July 26, a day after a Turkish court allowed Brunson to be moved out of prison and placed under house arrest, to threaten Turkey with “large sanctions” unless Brunson was released “immediately.” Pence had struck a similarly bellicose tone during a conference on religious freedom in Washington earlier that day.

Pence renewed the threat of sanctions in a July 29 tweet. Transferring the pastor to house arrest wasn’t “good enough,” Pence wrote. “The United States of America is prepared to bring sanctions against Turkey until Pastor Andrew Brunson is free.”