Kirby called Cumhuriyet "one of Turkey's most respected newspapers" and criticized Ankara's ongoing detention of many journalists
The United States issued a stern rebuke to its ally Turkey on Monday after authorities stepped up their persecution of media outlets critical of the government.
Washington regularly expresses concern about the increasingly authoritarian treatment of the media by President Recep Tayyip Erdogan's government.
But State Department spokesman John Kirby raised the tone after Turkey detained the editor of the newspaper Cumhuriyet and closed 15 other outlets.
"The United States is deeply concerned by what appears to be an increase in official pressure on opposition media outlets in Turkey," he said.
Kirby called Cumhuriyet "one of Turkey's most respected newspapers" and criticized Ankara's ongoing detention of many journalists.
He insisted Washington remains a friend of Turkey and supports its fight against terrorism, including its fight against the Kurdish PKK group.
But he added: "We encourage the government of Turkey to ensure that the rule of law and fundamental freedoms are protected.
"Democracies become stronger by allowing diverse expressions of views, particularly in difficult times," he argued.
Cumhuriyet's editor Murat Sabuncu was detained and police are hunting for executive board chairman Akin Atalay, Turkey's official news agency said.
The paper, which has published revelations embarrassing for the government, said at least a dozen journalists were detained in dawn raids.