ANCHORAGE, Alaska (AP) — A Russian submarine surfaced near Alaska on Thursday during a Russian war game exercise, U.S. military officials said.

It was unclear if the submarine was in distress.

The North American Aerospace Defense Command and U.S. Northern Command are closely monitoring the submarine, Northern Command spokesman Bill Lewis said.

“We have not received any requests for assistance from the Russian Navy or other mariners in the area,” Lewis said from Peterson Air Force Base in Colorado. “We always stand ready to assist those in distress.”

Lewis declined to provide further details about the submarine, including its proximity to Alaska. He only said it was operating in international waters near Alaska.

“We closely track vessels of interest, including foreign military naval vessels, in our area of responsibility,” Lewis said.

The Russian military exercise is taking place in international waters, well outside the U.S. territorial sea, he said.

The presence of Russian military assets in the war games caused a stir for U.S. commercial fishing vessels in the Bering Sea on Wednesday, the U.S. Coast Guard said.

“We were notified by multiple fishing vessels that were operating out the Bering Sea that they had come across these vessels and were concerned. So they contacted us,” Coast Guard spokesman Kip Wadlow said earlier Thursday.

The Coast Guard contacted the Alaskan Command at Joint Base Elmendorf-Richardson, which confirmed the ships were there as part of a pre-planned Russian military exercise that was known to some U.S. military officials, Wadlow said.

Wadlow did not have information about the scope of the exercise or how many Russian vessels were involved, referring those questions to the Alaskan Command.

Officials at the Anchorage base referred questions to Air Force officials at the U.S. Northern Command.