Turkey arrested 10 retired admirals on Monday after a letter signed by more than 100 of them talked about a possible threat to a treaty governing the use of Turkey's vital waterways.
Turkish President Recep Tayyip Erdogan said the statement in support of the Montreaux Convention, which regulates the passage of ships through the Bosporus and Dardanelles straits, went beyond freedom of expression.
"In a country whose past is filled with coups, (another) attempt by a group of retired admirals can never be accepted," Mr Erdogan said.
Ankara's approval last month of plans to develop a shipping canal in Istanbul comparable to the Panama or Suez canals has opened up debate about the 1936 maritime accord.
In their letter, the 104 retired admirals said it was "worrying" to open the Montreux treaty up for debate, calling it an agreement that "best protects Turkish interests".
“The fact that withdrawing from the Montreux Convention was opened to debate as part of talks on Canal Istanbul and the authority to exit from international treaties was met with concern,” the retired admirals said.
The Montreux Convention assures civilian vessels free passage through the Bosphorus and Dardanelles straits in peacetime. It also regulates the use of the straits by military vessels from non-Black Sea states.
The Ankara chief public prosecutor's office said it issued arrest warrants for 10 of the admirals and ordered four others to report to police within three days, opting not to detain them because of their age.
The admirals are being investigated on the charge of reaching "an agreement with the aim of committing a crime against the security of the state and the constitutional order", state-run Anadolu Agency reported.
Mr Erdogan's spokesman said the admirals' statement had the hallmarks of a military plot to overthrow the government.
"A group of retired soldiers are putting themselves into a laughable and miserable position with their statement that echoes military coup times," Ibrahim Kalin said.
"Stating one's thoughts is one thing. Preparing a declaration evoking a coup is another," Parliament Speaker Mustafa Sentop said on Sunday.
Coups are a sensitive subject in Turkey since the military, which has long seen itself as the guarantor of the country's secular constitution, staged three coups between 1960 and 1980.
There was also an attempted overthrow of Mr Erdogan in 2016, blamed on followers of US-based Muslim cleric Fethullah Gulen in the military.
One of the 10 suspects detained on Monday was Cem Gurdeniz, described as the father of Turkey's controversial new maritime doctrine known as "Blue Homeland".
The doctrine has grown in prominence, especially during tensions last year between Greece and Turkey over Ankara's gas exploration in the Eastern Mediterranean. It argues that Turkey has rights to substantial maritime borders including the waters surrounding some Greek islands, a claim Athens rejects.
