"The United States will impose large sanctions on Turkey for their long time detainment of Pastor Andrew Brunson," Trump said on Twitter. "He is suffering greatly. This innocent man of faith should be released immediately!"

Brunson was transferred to house arrest Wednesday after being detained in the Aegean province of Izmir in December 2016. He was charged with spying for the PKK, a designated terrorist group in the U.S. and Turkey, and the Fetullah Terrorist Organization (FETO), the group Turkey accuses of being behind the defeated July 2016 coup attempt.

Earlier, Vice President Mike Pence threatened via Twitter to impose "significant sanctions on Turkey until this innocent man of faith is free."

The Izmir 2nd High Criminal Court cited Brunson's health in its decision to transfer him to house arrest.

The court decided to allow Brunson to live at his home address in Izmir, but barred him from "abandonment of residence" and also imposed a ban on him leaving the country.

After the decision, the cleric left prison with a police escort after completing certain procedures.

Extensive security measures have been taken at the Brunson residence.