The Maritime Self-Defense Force and the U.S. Navy are conducting a joint military exercise in the East China Sea, a Japanese government source said Friday.

The drill, which started Tuesday and was to finish Friday, involves MSDF destroyers and a U.S. Navy carrier strike group including the nuclear-powered aircraft carrier Carl Vinson, the source said.

Tensions remain high in the sea, where China has repeatedly sent vessels into Japanese waters near the Senkaku Islands. The uninhabited islets are controlled by Japan but claimed by China, which calls them Diaoyu.

The rare use of a U.S. aircraft carrier in an East China Sea drill indicates a message is being sent to China, as well as to North Korea, which has repeatedly carried out banned ballistic missile launches.

Chief Cabinet Secretary Yoshihide Suga, the government's top spokesman, refrained from confirming the drill on Friday.

According to the source, the joint exercise includes tactical and communication exercises. A senior Defense Ministry official said the drill does not involve the MSDF exercising its expanded powers granted under controversial security legislation that took effect last year.

The exercise is part of an ongoing joint drill between the United States and South Korea. The two-month Foal Eagle field training exercise, which began at the start of this month, involves ground, air and naval forces.

In December last year, China sailed its first aircraft carrier Liaoning through the Miyako Strait between the islands of Okinawa and Miyako. Chinese fighter aircraft and bombers also flew through the strait last week as part of an exercise.

On Monday, North Korea launched four ballistic missiles in Japan's direction nearly simultaneously, with one falling into the Sea of Japan as close as 200 km from the shore.