Metin Gurcan, a founder of the Turkish opposition Democracy and Progress Party (DEVA), said on Friday he had been detained over "political espionage" and that police were raiding his house.
Gurcan, a retired member of the Turkish Armed Forces, helped establish the Deva Party with Ali Babacan, a former deputy prime minister and minister under President Tayyip Erdogan Erdogan. Gurcan is also a prominent defence analyst.
"I am being detained on charges of political espionage. The police are in the house... They are searching. I am shocked. I want your help," Gurcan said on Twitter, without elaborating.
Turkish police were not immediately available for comment.
Speaking in Istanbul, Babacan said his party backs Gurcan and its lawyers would provide him with support "until the end", adding they were seeking more details.
"If the move today is political in nature, or if the target is a particular stance against our party, an attempt to mask the grave economic conditions in the country, I would like to state that such attempts will never deter the Deva team," he said, in reference to a historic slide in the lira this week.
The lira has plunged to all-time lows and lost as much as 25% of its value since the beginning of last week over concerns about aggressive interest rate cuts backed by Erdogan. read more
Polls show support for Deva, founded in March 2020, around 2%, while support for Erdogan and his AK Party are at multi-year lows. Turks have cited economic mismanagement among the key factors.
Deva and other opposition parties have called for urgent elections amid the lira meltdown, but the government has said presidential and general elections would be held as planned in June 2023.
Reporting by Tuvan Gumrukcu; Editing by Jonathan Spicer and Barbara Lewis