REUTERS

Crying out the names of their loved ones as they scattered flower petals into the ocean, relatives of the 53 Indonesian navy crew members who died in a sunken submarine paid tribute at a ceremony at sea on Friday.

Servicemen in white navy uniforms holding ceremonial swords saluted in unison on the deck of the multi-purpose hospital ship KRI Dr. Soeharso, in a mark of respect to the victims at the location where the submarine was last seen.

The KRI Nanggala-402 was discovered at a depth of nearly 840 metres (2,756 ft) on Sunday, broken into at least three parts, four days after it lost contact while preparing to conduct a torpedo drill.

Around 150 family members attended the memorial aboard the ship. Some wept and tried to console each other.

Retrieval operations are still ongoing for German-built submarine, with help from international search teams, as authorities struggle to figure out how to lift the wreckage.

"The position of the KRI Nanggala has remained in the area with no movement detected," Navy Chief of Staff Yudo Margono told reporters.

"We are looking at experiences of other countries, such as lifting using special ropes or using air balloons. We still don't know which approach to use," Yudo said.

Experts have said bringing the submarine to the surface will be a huge challenge requiring specialised salvage equipment.

The Nanggala was one of five submarines operated by Indonesia - two German-built Type 209s and three newer South Korean vessels.

The military has been seeking to modernise its defence capabilities but some of its equipment is old and there have been fatal accidents in recent years.