Jakarta, May 19 (IANS): Indonesia's navy said that an operation to retrieve parts of a submarine that sunk with 53 people on board last month has been able to pull up two life rafts from the bottom of the sea.

The German-made KRI Nanggala-402 lost contact during a torpedo firing exercise on April 21. An international search team involving Singapore, Australia and Malaysia found the submarine four days later, sunken and broken into three at a depth of more than 800 metres north of Bali, DPA reported.

Indonesian navy second fleet commander Rear Admiral Iwan Isnurwanto said on Tuesday that each of the life rafts weighed 700 kilograms.

The life rafts are being stored in one of the six Indonesian navy ships that are taking part in the recovery operation, along with China's three ocean salvage rescue and scientific research ships.

"The operation team tried to lift the sail section twice but failed. The team deployed a robot to attach strings to the sail section, but the strings broke as it was being lifted. It may be because it weighed more than our initial estimate of 18 tonnes," Isnurwanto said. He added that the operation would also try to lift the stern section, on which the submarine's radar is still attached.

No human remains of all the submariners who died in the accident were found. The Indonesian navy has pledged that it would continue the operation until the remains of the commander, 49 crew members and three gunners are located and retrieved.