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The US has imposed sanctions on Turkey's justice and interior ministers over the continued detention of pastor Andrew Brunson.
The evangelical from North Carolina has been held for nearly two years over alleged links to political groups.
"We believe he's a victim of unfair and unjust detention," White House press secretary Sarah Sanders said.
Last week President Trump warned Turkey it would face "large sanctions" if it did not release Mr Brunson immediately.
Speaking to reporters on Wednesday, Ms Sanders said: "We've seen no evidence that Pastor Brunson has done anything wrong."
She added that the two Turkish ministers had both played "leading roles" in the arrest of the US pastor.
"As a result, any property or interest in property of both ministers within US jurisdiction is blocked and US persons are generally prohibited from engaging in transactions with them," she said.
The Turkish foreign ministry has previously described US demands to release Mr Brunson as "unacceptable".
Who is Andrew Brunson?
Mr Brunson is a long-term resident in Turkey. He lived with his wife and three children while working as the pastor of the small Izmir Resurrection Church, which had a congregation of about two dozen.
The authorities accuse him of having links with the outlawed Kurdistan Workers' Party (PKK) and the Gulenist movement, which Turkey blames for a 2016 failed coup.
Mr Brunson has denied charges of espionage, but faces up to 35 years in jail if found guilty.
He was moved into house arrest last month for health reasons, but US Secretary of State Mike Pompeo said this was not enough.
"We have seen no credible evidence against Mr Brunson," Mr Pompeo tweeted at the time.
Turkey's foreign ministry said it had shared "necessary information" with the US, but insisted the case should be left with its judiciary.