The US military is sending airborne assistance to aid Indonesia’s search for a missing submarine with 53 crew.
Indonesian authorities estimate they have just hours left to find the navy submarine before the oxygen runs out.
The KRI Nanggala 402 disappeared on Wednesday during exercises off the coast of Bali, sparking a frantic search to locate the stricken vessel.
An oil slick where it was thought to have submerged suggested damage to a fuel tank may have been a factor.
Pentagon spokesman John Kirby said the US was “deeply saddened” by the turn of events.
“Our thoughts are with the Indonesian sailors and their families,” Mr Kirby said in a statement. “At the invitation of the Indonesian government, we are sending airborne assets to assist in the search for the missing submarine.”
The Indonesian military said late on Thursday night that it had detected signs of an object at a depth of between 50 and 100 metres (165 to 330 feet), and had deployed ships with sonar-tracking equipment in the hope it was the KRI Nanggala 402.
“We’ve only got until 0300 tomorrow [Saturday] so we’re maximising all of our efforts today,” said Indonesian military spokesman Achmad Riad. “Hopefully there will be a bright spot.”
At least six warships, a helicopter and 400 people have since been involved in the search. Singapore and Malaysia have dispatched ships to the area, and Australia, France and Germany have also offered assistance.
“We keep waiting, we keep praying,” Ratih Wardhani, whose brother Major Wisnu Subiyantoro among the crew, said.
“We hope that God will ease the effort of the joint rescue team from the Indonesian Navy and other countries, and they will successfully bring the Nanggala submarine with its 53 personnel to reunite with their families happily,” she said.
“That is our hope. We can only support them with our prayers and our optimism that they will return.”
The KRI Nanggala 402 lost contact shortly after requesting permission to dive during live torpedo exercises early on Wednesday morning. The German-built vessel is one of five submarines operated by Indonesia. It was made in the late 1970s, and underwent a two-year refit in South Korea that was completed in 2012.
A navy spokesman told the BBC the incident was the first time Indonesia had lost one of its submarines. But similar incidents have happened elsewhere.
In 2000, the Kursk, a Russian navy sub, sank during manoeuvres in the Barents Sea with the loss of all 118 crew. An inquiry found that one torpedo had exploded, detonating all the others. Most of the Kursk’s crew died instantly but some survived for several days before suffocating.
In 2003, 70 Chinese naval officers and crew were killed in an accident on a Ming-class submarine during exercises.
And in 2017, an Argentine military submarine went missing in the southern Atlantic with 44 crew on board. Its wreck was located a year later and officials said the submarine had imploded.