Tensions are rising in the East China Sea after China deployed an armed, former navy frigate for the first time to challenge Japan’s control of contested islands in what may be an attempt to shift Tokyo’s attention away from disputes in the South China Sea.

Three ships including the frigate still equipped with gun turrets and now operated by the Chinese coast guard sailed within the 12-mile exclusion zone that Japan claims around the islands on Dec. 26, said a Japanese foreign ministry official who asked not to be named, citing government policy. Japan lodged an official protest over the incident.

The escalation in the East China Sea comes at a time of heightened tensions in the South China Sea after the U.S. Navy began freedom of navigation patrols there to challenge China’s claims in territorial contests with the Philippines and Vietnam. Japan is home to the U.S. Seventh Fleet, which is leading the patrols, and backs the U.S. effort. China has repeatedly urged Prime Minister Shinzo Abe to stay out of the South China Sea dispute.

… China is interested in tying “Japan’s focus to the East China Sea in case Tokyo might ‘mistakenly’ believe that the situation has already abated in the East China Sea so that it can start looking at the South China Sea,” said Collin Koh Swee Lean, an associate research fellow at the S. Rajaratnam School of International Studies in Singapore.