ISTANBUL  Thousands of people protested in two Turkish cities on Friday in response to the detention this week of seven journalists, a development that has prompted new expressions of concern from Europe and the United States about the state of press freedom in Turkey.

Protesters in Ankara and Istanbul, many of them media workers, called for an end to what they called repression of Turkish journalists and chanted in support of Nedim Sener of the newspaper Milliyet, a frequent critic of the government, and Ahmet Sik, who is known for his reporting on human rights abuses and on what he says are illegal Islamic networks operating within the Turkish state.

“Pressure on journalists has reached an intolerable limit,” Ercan Ipekci, head of the Turkish Journalists Syndicate, said during the demonstration in central Istanbul. “We expect democratic steps to be taken and substantial changes made to the penal code to lift away this environment of fear and pressure imposed upon journalists.” An umbrella group called the Freedom for Journalists Platform organized the protests in both cities.

Mr. Sener and Mr. Sik were among seven journalists detained Thursday on suspicion of belonging to a shadowy network known as Ergenekon, which Turkish prosecutors say has plotted to overthrow the pro-Islamic Justice and Development Party’s government. As of Friday, none of the seven were known to have been charged with any crime.