Mr. Erdogan, in a televised speech on Friday, vowed to pursue members of the so-called parallel structure, which he said had challenged his rule with a corruption inquiry last year, as well as at other times. “We have gone into their lairs, and we will go into them again,” he said. “Whoever is beside them and behind them, we will bring down this network and bring it to account.”

The corruption investigation implicated many of those close to Mr. Erdogan, then the prime minister. The inquiry led to resignations of three ministers and was regarded as the biggest threat to the rule of Mr. Erdogan after more than a decade in power. Mr. Gulen, who was a close ally of Mr. Erdogan for years before a falling out, denied having any role in the investigation.

After the investigation, thousands of police officers and prosecutors were removed from their positions in what was seen by many as an attempt by Mr. Erdogan to eliminate Mr. Gulen’s influence in the state structure. Senior judicial bodies were also restructured in a manner that, critics say, paved the way for corruption charges to be dropped in September against 96 suspects, who were Erdogan supporters.

The detentions on Sunday drew more than 1,000 people outside Zaman’s headquarters to protest repression of the news media.

“This is a reckless move toward dictatorship,” Cengiz Candar, a journalist critical of the government, wrote on his Twitter account. “It is nothing else than a rough attack against media freedoms with the pretext of a ‘community operation.’ ”

A State Department spokeswoman, Jen Psaki, said in a statement: “Media freedom, due process and judicial independence are key elements in every healthy democracy and are enshrined in the Turkish Constitution. As Turkey’s friend and ally, we urge the Turkish authorities to ensure their actions do not violate these core values and Turkey’s own democratic foundations.”

Senior officials of the European Union, which Turkey hopes to join, issued a strongly worded statement, calling the detentions “incompatible with the freedom of media, which is a core principle of democracy.”