U.S. Coast Guard tracked two Chinese ships bound for the Arctic last week, the Coast Guard said late Friday.

A Chinese research ship transited north through the U.S. “exclusive economic zone” – known as the EEZ – and over the extended continental shelf in the Bering Sea with a declared destination of the Arctic. A second China-flagged research vessel also transited to the Arctic.

For the first time this year, Chinese vessels were tracked transiting through the U.S. exclusive economic zone and over the extended continental shelf (i.e., continental shelf beyond 200 nautical miles of shore) in the Bering Sea.

“In response, the U.S. Coast Guard Cutter Munro (WMSL 755) executed Operation Frontier Sentinel to actively monitor the vessels during their northbound transit,” the Coast Guard said in a statement. “This operation is designed to protect American sovereign rights, ensure consistency with international law, and position the Coast Guard to rapidly respond to any detected malign activity.”

Under international law, foreign vessels are permitted to operate within the U.S. EEZ and over the U.S. extended continental shelf.

“The Coast Guard remains vigilant to ensure their activities comply with established international law,” the Coast Guard stressed. “In particular, conducting marine scientific research within the U.S. EEZ and/or on the U.S. extended continental shelf would require advance permission from the United States and subsequent sharing of information collected.”

Rear Adm. Bob Little, commander U.S. Coast Guard Arctic District, said in a statement Friday that the coast guard alongside the department of war, department of state, and international partners is actively responding to competitor activities across an increasingly contested Arctic.