Turkish authorities have detained nine crew members of the tanker Alsu following a collision with the cargo ship Tugberk Imamoglu in the Sea of Marmara, as search operations continue for 10 missing seafarers.

The two Turkish-flagged vessels collided early September 2 about 18 nautical miles south of Silivri, near Istanbul. The Tugberk Imamoglu, carrying about 4,200 tons of steel products, reportedly sank within about 10 minutes, while the Alsu was empty and showed no visible damage above the waterline.

Prosecutors said radio records indicate that the captains of the two vessels communicated before the collision and were discussing how they would pass each other. Nine of the Alsu’s 10 crew members, excluding the cook, were detained as part of the investigation, while authorities secured navigation, radar and communication records for examination.

Search teams have recovered a lifeboat, life rings and other debris, but the 10 crew members of the Tugberk Imamoglu, all Turkish nationals, remain missing. Authorities believe the wreck may be lying at a depth of about 900 meters and are coordinating with the Turkish Navy for further underwater search operations.