Turkey on Monday detained 10 retired admirals after they openly criticised a canal project dear to President Recep Tayyip Erdogan in a country where the hint of military insubordination raises the spectre of past coups.
The official approval last month of plans to develop a 45-kilometre (28-mile) shipping lane in Istanbul comparable to the Panama or Suez canals has opened up debate about Turkey's commitment to the 1936 Montreux Convention.
In their letter, 104 retired admirals said the existing treaty "best protects Turkish interests".
"Recently, the opening of the Montreux Convention to debate within the scope of the authority to withdraw from international treaties and the Canal Istanbul project is a cause for concern," the letter read.
Erdogan on Monday accused the 104 retired admirals of "hinting at a political coup" by criticising his plans for a new canal linking the Black Sea to the Mediterranean.
"In a country whose past is filled with coups, (another) attempt by a group of retired admirals can never be accepted," said Erdogan in a statement.
While the Ankara chief public prosecutor's office has issued arrest warrants for 10 former admirals who signed the letter, four others had to report to police in the Turkish capital within three days since the prosecutor opted not to detain the other four due to their advanced age.
They are accused of "using force and violence to get rid of the constitutional order", NTV broadcaster reported.
Father of sea doctrine
The prosecutor's office opened a probe on Sunday into the retired admirals on suspicion of an "agreement to commit a crime against the state's security and constitutional order".
The wording is similar to that prosecutors have used against other Erdogan critics who have been jailed in a crackdown that followed a failed putsch in 2016.
The retired admirals detained on Monday included some of Turkey's most famous naval commanders.
They included Cem Gurdeniz, often 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 Turkey has rights to substantial maritime borders including the water surrounding some Greek islands, much to Athens' chagrin.
Also detained was Alaettin Sevim, who had previously been arrested in 2011 as part of the so-called Ergenekon alleged coup plot against the government, which was later discredited.
Before the arrest warrants were issued, state news agency Anadolu said the prosecutor's office had determined who the "leaders" were of the open letter.
Turkish officials have reacted angrily to the letter, claiming it appears to be a call for a coup.
"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.
The attempt to overthrow Erdogan in 2016 was blamed on followers of US-based Muslim preacher Fethullah Gulen in the military.
"This is upsetting in the name of democracy," Turkish Justice Minister Abdulhamit Gul said on Monday.
"Our struggle against this dark mentality continues. The necessary response will be given within a legal framework," Gul added.
Erdogan's proposed 75-billion-lira ($9.8-billion) alternative to the Bosphorus and Dardanelles raises questions on whether existing agreements would apply to the new route.
Last month, parliament speaker Sentop said the president "could" withdraw from the convention.
"He has the power," he told HaberTurk channel on March 24. "But there is a difference between possible and probable."
Erdogan assumed the power to pull Turkey out of treaties without parliament's approval in 2018.
Last month he withdrew Turkey from the world's first binding treaty to prevent and combat violence against women.
(FRANCE 24 with AFP)