Turkish police detained two opposition journalists as part of an investigation into "political and military espionage", the official Anadolu news agency reported on Monday.
Details of the detentions were not immediately clear, but other media reported they may be linked to reporting about Turkey's involvement in conflicts in Libya and Syria.
Ismail Dukel from Tele1 TV Ankara and Muyesser Yildiz, news coordinator at OdaTV online news site, were taken into custody on Monday and are being questioned by the anti-terror police in Ankara, Anadolu said.
Telel editor-in-chief Merdan Yanardag confirmed the detentions on his Twitter account and said they were aimed at giving an "ultimatum to independent media".
"We are at the top of our jobs. We will not remain silent and we will not bow," he said.
Anadolu did not elaborate on the detentions, saying only they were for "political and military espionage".
Pro-government Sabah newspaper reported that the journalists were accused of leaking information about Turkey's war plans in Libya and Syria.
It said Yildiz held "critical phone talks" with a military personnel - identified as EB - about Turkey's military units in Libya, adding that the E.B. was also detained in Istanbul in connection with the same dossier on Monday.
Turkey backs rebels looking to oust President Bashar Al Assad in Syria and has carried out three military incursions against the Islamic State and Syrian Kurdish militia forces deemed as terror group by Ankara.
In Libya, Turkey supports the UN-recognised government in Tripoli which has recently made gains against Field Marshal Khalifa Haftar.
The latest journalist detentions are not the first in connection with reporting on Turkey's military activities.
In March, Turkish authorities arrested OdaTV news editor Baris Terkoglu, reporter Hulya Kilinc and editor-in-chief Baris Pehlivanoglu on suspicion of disclosing the identity of a Turkish intelligence agency official.
The story also said that the officer was killed in Libya in February.
Turkey ranks 154 out of 180 countries on Reporters Without Borders' 2020 World Press Freedom index.
According to the P24 press freedom group, there are 103 journalists behind bars in Turkey, many arrested in a crackdown after a coup attempt in 2016.