TOKYO (Kyodo) -- The U.S. Navy conducted in December a so-called freedom of navigation operation in southwestern Japan waters, in a move that disagrees with Tokyo's claims of sovereignty.
According to the U.S. 7th Fleet, the Dec. 15 operation involved the navy's Alan Shepard supply vessel sailing in the vicinity of the Tsushima Strait between Kyushu, one of Japan's main islands, and South Korea. Its shipboard helicopter also flew.
The move is seen as emphasizing the U.S. stance to abide by the international rules-based order in a veiled alert to China, which has become increasingly assertive in the East and South China seas, by equally disagreeing with its ally Japan over its claims.
The Alan Shepard conducted "normal operations within claimed territorial seas to challenge excessive maritime claims and preserve access to the waterways as governed by international law," the 7th Fleet has said.
The Japanese government has argued that its maritime territory is based on a "straight baseline method" in accordance with the U.N. Convention on the Law of the Sea, used when there are indentations or islets or islands close to the coast. Its application of the method in 1997 has allowed it to expand its maritime claims.
The United States believes that the low-water line along the coast counted during a low tide is more appropriate.
Shigeki Sakamoto, a professor emeritus at Kobe University in international law, said, "The United States is opposed to a bold straight baseline method, since it also affects the airspace above the territorial sea."
The December operation signals the United States is severe even against an ally's interpretation, he said.
The United States has asserted its rights to navigate similarly in various waters around the world, and has conducted such operations several times in the vicinity of the Tsushima Strait and in the East China Sea since the late 1990s.