The official approval last month of plans to develop a new 45-kilometre (28-mile) shipping lane in Istanbul comparable to the Panama or Suez canals has raised questions over Turkey's commitment to the Montreux Convention.

The 1936 pact is aimed at demilitarising the Black Sea by setting strict commercial and naval rules on passage through the Bosphorus and Dardanelles straits leading to the Mediterranean.

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.

- Father of sea doctrine -

The Ankara chief public prosecutor's office issued arrest warrants for the 10 and ordered four other suspects to report to the capital's police within three days, opting not to detain them because of their age.

They are accused of "using force and violence to get rid of the constitutional order", NTV broadcaster reported.

The wording is similar to what prosecutors have used against other Erdogan critics 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".

Gurdeniz is known as a "Eurasianist", a group also believed to be present in the Turkish military.

Eurasianists' approach to foreign policy is anti-Western, advocating improved relations with China, Iran and Russia, which could undermine Turkey's position within the NATO military alliance.

Some analysts however believe Erdogan's proposed 75-billion-lira ($9.8-billion) canal poses a threat to Moscow because it could offer NATO powers unfettered access to the Black Sea, where Russia has seized Ukraine's Crimea peninsula.

The project is of concern to Russia because it "could introduce any amount of warships at any time into the Black Sea", James Goble wrote for the Jamestown think-tank last year.

This would "both encourage other littoral states to look away from Moscow and ostensibly threaten Russian national security," Goble said.

- 'Evoking coups' -

Turkey has not officially stated its position on whether it believed the Montreux Convention would apply to the proposed canal.

Last month, parliament speaker Mustafa Sentop said the president "has the power" to withdraw Turkey from the treaty.

"But there is a difference between possible and probable," the speaker told HaberTurk channel on March 24.

Erdogan assumed the power to pull Turkey out of treaties without parliament's approval in 2018.

But while much around the proposed canal and the fate of the 1936 treaty remains shrouded in mystery, Turkish officials reacted to the retired admiral's letter with fury, claiming it appeared to be a call for a coup.

"This is upsetting in the name of democracy," Turkish Justice Minister Abdulhamit Gul said on Monday.

Coups are a sensitive subject in Turkey because 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.

- Opposition anger -

The retired admirals' letter was published a day after 126 former Turkish ambassadors signed a similar appeal for the treaty to be retained.

But Erdogan's critics accused the government of trying to use their outrage over the letter to distract from Turkey's faltering economy.

Inflation is a particular worry for many. A new reading on Monday showed it reaching 16.2 percent in annual terms last month, up from 15.6 in February.

"In fact the issue is not Montreux but the economy," Suat Kiniklioglu, a former ruling party lawmaker, tweeted.

"This is the new normal. To remain in power in a state of permanent crisis," Kiniklioglu, now an analyst, said.