The Indonesian Navy submarine KRI Nanggala takes part in a drill off Cilegon, Indonesia, in this Oct 3, 2017 photo. Indonesia's navy is searching for the KRI Nanggala submarine that went missing north of the resort island of Bali with a number of people on board, the military said April 21, 2021. (PHOTO / AP)

Indonesian rescuers searching for a submarine that went missing with 53 people on board found an oil spill on Wednesday near its dive location, authorities said.

The 44-year-old submarine, KRI Nanggala-402, was conducting a torpedo drill in waters north of the island of Bali but failed to relay the results as expected, a navy spokesman said.

An aerial search found an oil spill near the submarine's dive location and two navy vessels with sonar capability have been deployed to assist the hunt, Indonesia's Defense Ministry said.

A ministry statement said requests for assistance had been sent and Australia, Singapore and India had responded

A ministry statement said requests for assistance had been sent and Australia, Singapore and India had responded.

CNN Indonesia reported that Indonesian navy official Julius Widjojono said he suspected the submarine had descended to a depth of 600-700 meters.

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"We are still searching in the waters of Bali, 60 miles (96 km) from Bali, (for) 53 people," military chief Hadi Tjahjanto told Reuters in a text message. He said contact with the vessel was lost at 4:30 am on Wednesday.

Representatives of the defense departments of Australia and Singapore did not immediately respond to requests for comment.

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The military chief will hold a media briefing to share further information about the search on Thursday from Bali, a spokesman said.

The 1,395-ton KRI Nanggala-402 was built in Germany in 1977, according to the defense ministry, and joined the Indonesian fleet in 1981. It underwent a two-year refit in South Korea that was completed in 2012

Military analyst Soleman Ponto said it is too early to determine the fate of the submarine conclusively.

"We don't know yet whether the communication equipments were broken or the submarine has sunken. We have to wait for at least three days," he said.

The 1,395-ton KRI Nanggala-402 was built in Germany in 1977, according to the defense ministry, and joined the Indonesian fleet in 1981. It underwent a two-year refit in South Korea that was completed in 2012.

Indonesia in the past operated a fleet of 12 submarines purchased from the Soviet Union to patrol the waters of its sprawling archipelago.

But now it has a fleet of only five including two German-built Type 209 submarines and three newer South Korean vessels.

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Indonesia has been seeking to modernize its defense capabilities but some of its equipment still in service is old and there have been deadly accidents in recent years.

In 2016, an Indonesian air force transport plane crashed into a mountain, killing all 13 people board, during a training exercise in the remote region of Papua.

In 2015, an Indonesian military transport plane crashed into a northern residential area two minutes after takeoff, killing more than 100 people.