The Federal Bureau of Investigation said there was no immediate evidence of terrorism or sabotage, but a security alert was in force at the installation because the circumstances surrounding the deaths were unclear. FBI and Coast Guard officials declined to say whether investigators believed they were dealing with a double homicide or a murder-suicide.

The deaths marked the first fatal shootings at a Coast Guard facility in Alaska in over a decade.

“Since we don’t have all the details, we strongly advise that all Kodiak residents remain vigilant and report any suspicious activity to local law enforcement officials,” Capt. Jesse Moore, base commanding officer, said in a statement soon after the slayings were first reported.

“We are deeply saddened that we lost two shipmates. This is a rare occurrence, and we are going to do everything possible to ensure we find out exactly what happened.” The Coast Guard declined to identify or give any details about the dead until their next of kin had been notified.

The Guardsmen were found fatally shot on Thursday at a communications station on the outskirts of Coast Guard Base Kodiak, about 400 km southwest of Anchorage.

Authorities were looking for a potential suspect who might be at large, the Coast Guard said. But by day’s end, lockdowns and other security precautions placed in effect at nearby schools on Thursday had been lifted, school officials said.

Anchorage television station KTUU reported that the two dead were believed to have been shot sometime between 7 a.m. and 8 a.m. local time, and that a third individual might have been involved.

Communications Station Kodiak is one of 13 units making up the Kodiak base, which also includes an air station and naval facilities and is the hub of operations for Coast Guard in the region.