Donald Trump has threatened NATO ally Turkey with "large sanctions" unless a US pastor held on terrorism and spying charges is released.
Tweeting from on board Air Force One, Mr Trump said: "The United States will impose large sanctions on Turkey for their long time detainment of Pastor Andrew Brunson, a great Christian, family man and wonderful human being."
He said Brunson "is suffering greatly. This innocent man of faith should be released immediately!"
Earlier, Vice President Mike Pence said that if Turkey does not take immediate action to free Mr Brunson "the United States of America will impose severe economic sanctions on Turkey."
Pence was speaking at the close of a three-day conference on religious freedom.
Mr Brunson, 50, an evangelical Christian pastor originally from North Carolina, was let out of jail on Wednesday after 18 months to serve house arrest because of "health problems", according to Turkey's official Anadolu news agency.
Mr Trump has repeatedly demanded Mr Brunson's release and said on Twitter last week that the pastor's detention was "a total disgrace".
"Brunson is an innocent man, there is no credible evidence against him," Mr Pence said.
Neither Trump nor Pence elaborated on the type of sanctions the US could impose but the threat has already prompted a downturn in Turkey's financial markets. There was no immediate comment from US lawmakers who have threatened to withhold weapons sales to Turkey as strains have escalated over Brunson's detention.
In response, a spokesman for Turkish President Tayyip Erdogan said Washington's threats were unacceptable and damaging to the US-Turkey alliance.
"The United States must reconsider its approach and adopt a constructive position before inflicting further damage to its own interests and its alliance with Turkey," Erdogan's spokesman, Ibrahim Kalin, said in a written statement.
Turkish Foreign Minister Mevlut Cavusoglu spoke to US Secretary of State Mike Pompeo on Thursday, according to Turkish foreign ministry sources.
If convicted, Mr Brunson faces up to 15 years in prison for "committing crimes on behalf of terror groups without being a member", references to outlawed Kurdish militants and the network of a US-based Muslim cleric blamed for a failed coup attempt.
He could receive another 20 years if he is found guilty of espionage. Mr Brunson strongly denies the charges.
At the end of a recent hearing, the court inside a prison complex in western Turkey rejected Mr Brunson's lawyer's request that he be freed pending the outcome of the trial.
His case was adjourned until October 12.
