Mike Pompeo also said he expects talks to take place between American and Turkish officials this week about the future of Andrew Brunson.
Speaking with reporters in New York on Monday, Mr Pompeo said: "Yes, he could be released this month.
"He should have been released last month.
"And he should be released today, in fact.
"We have talked to the Turks.
"They know the expectations."
Mr Brunson (pictured below with his wife, Norine) had been leading a small church in the coastal city of Izmir for more than 20 years before he was arrested in October 2016 and later charged with espionage and terrorism offences. He faces up to 35 years in prison. Mr Brunson denies any wrongdoing.
The 50-year-old from Black Mountain in North Carolina is accused of links to a movement spearheaded by Fethullah Gülen, a cleric Turkey considers responsible for an attempted coup in July 2016.
Thousands of people including judges, soldiers and teachers were suspended in a subsequent crackdown by authorities.
The detention of Mr Brunson has drawn condemnation from President Donald Trump and prompted him to double import tariffs on Turkish steel and aluminium.
Recep Tayyip Erdogan, the Turkish President, is also visiting the US this week for a meeting at the United Nations.
Turkish presidential spokesman Ibraham Kalim was quoted as saying a decision on whether to free Andrew Brunson lies with the courts.
Mr Kalin added: "Obviously, we want to have good relations with every country, including the United States, but we have to resolve the issues between the two countries through diplomacy".
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