Japan and the United States held a joint exercise involving their Aegis-equipped ships in the Sea of Japan on Tuesday, amid heightened tension over North Korea.

The Maritime Self-Defense Force had already conducted an exercise involving its destroyers and the U.S. nuclear-powered carrier Carl Vinson on Sunday and Monday in the Philippine Sea.

As the U.S. carrier is believed to be approaching waters near the Korean Peninsula, the MSDF is considering holding another joint drill in the Sea of Japan, according to a Japanese government source. It is rare for the MSDF to hold an exercise with a U.S. carrier in the waters.

The exercise on Tuesday, apparently to confirm readiness for possible ballistic missile launches by North Korea, involved the MSDF destroyer Chokai and U.S. guided-missile destroyer Fitzgerald, according to the MSDF.

The Fitzgerald, which is part of the U.S. 7th Fleet and based at the Yokosuka Naval Base in Kanagawa Prefecture, was apparently already in the Sea of Japan monitoring North Korea prior to the exercise. The Chokai belongs to the MSDF’s Sasebo base in Nagasaki Prefecture.

Noting that the U.S. Navy is also conducting a maritime exercise with South Korea, the 7th Fleet said in a statement, “Both exercises demonstrate a shared commitment to security and stability in Northeast Asia as well as the U.S. Navy’s inherent flexibility to combine with allied naval forces in response to a broad range of situations.”

MSDF officials said the Japanese and U.S. destroyers practiced sharing information on missile interception and other communications.

The drill did not include training related to Japanese forces’ guarding of U.S. naval vessels when the two countries are jointly engaged in monitoring North Korean missile launches, a new role allowed under Japanese security legislation that came into effect last year.

North Korea on Tuesday marked the 85th anniversary of the founding of its armed forces without conducting another nuclear test or major missile launch, as feared. It did, however, carry out a large-scale firing drill around the eastern port city of Wonsan, according to South Korea’s military.