The purpose of the exercise was "to boost their tactical capability," the Japanese defense ministry said in a statement, without giving more details on the geographical location of the drills.

The three vessels will stop at Cam Ranh Bay in Vietnam over the weekend to replenish supplies, the statement said.

Nearly all of the energy-rich waters of the South China Sea are claimed by China, which has established military outposts on artificial islands in the area. Vietnam calls the waters the East Sea.

The United States has accused China of militarizing the South China Sea and trying to intimidate Asian neighbors who might want to exploit the area’s extensive oil and gas reserves.

China’s state-backed Global Times newspaper, noting the latest Japanese drills, said on Saturday that the frequent conducting of military activities in the South China Sea is not conducive to the security and stability of the area, and is firmly opposed by China.

The Chinese People’s Liberation Army has always kept a high level of alert, defending China’s national sovereignty, security and development interests, said the newspaper, which is published by the People’s Daily, the official newspaper of China’s ruling Communist Party.

The Global Times said Japanese warships had recently carried out activities in the South China Sea, with a helicopter aircraft carrier spotted on satellite on September 5.