A Navy submariner remains unaccounted for after going missing in Singapore on Sunday, according to service officials.

Machinist Mate Fireman Seth Woods, a crew member aboard the attack submarine Oklahoma City, was reported missing after separating from a group of other sailors while on shore liberty, according to Lt. Pah Yip, a spokesman for Submarine Group 7.

“The U.S. Navy is cooperating with local law enforcement authorities in Singapore and we hope to locate the Sailor soon,” he said. “His safety is our top priority.”

Woods, 18, hails from Tennessee, according to Pam Beharry, who said she is the missing sailor’s great aunt and answered messages to a Facebook page set up to spread the word about his absence.

A post on the “Missing US seaman in Singapore/Searching for Seth Woods” page states that Woods was “outside of a 7-Eleven store when his buddy went inside for a short period. When the buddy returned Seth was nowhere to be found.”

“Anything we can do to get Seth back to us safe is all that matters,” Beharry said in a Facebook message.

The Guam-based submarine Oklahoma City arrived in Singapore on May 3, the second Singapore visit of its deployment, according to a Navy press release.