The U.S. chief of naval operations highlighted the military partnership with Japan yesterday against a backdrop of tensions over U.S. troops on Okinawa and the March sinking of a South Korean warship, reportedly by North Korea.

Adm. Gary Roughead said Japan’s Maritime Self-Defense Force is a regional and global partner with the United States.

The U.S.-Japan Treaty of Mutual Cooperation and Security was signed 50 years ago.

"Fifty years of an alliance that has done so much to provide for the security, the stability, the prosperity of a region that is so important to the entire world," Roughead said.

He added that "there are no other two navies in the world that operate at the level of sophistication that we do."

The U.S. postponed anti-submarine warfare training with South Korea and exercises with the aircraft carrier George Washington after China objected, according to reports.

The South Korean frigate Cheonan was sunk on March 26. South Korea said an investigation concluded that North Korea torpedoed the ship, killing 46 sailors.

An international team of investigators from Australia, Great Britain, Sweden and the U.S. assisted South Korean experts in examining evidence from the sinking, the Pentagon said.

Roughead said the U.S. Navy has had stepped-up anti-submarine warfare training "for quite some time." He declined to talk about plans with South Korea.

"We continue to exercise with our partners and with our allies in the region," Roughead said. "With respect to the future exercises that we will hold with the Republic of Korea, I will not speculate on that at this time."

Roughead was in Hawaii to meet with Adm. Keiji Akahoshi, chief of staff for Japan’s Maritime Self-Defense Force, and Adm. Patrick Walsh, head of U.S. Pacific Fleet at Pearl Harbor.

About 190 Japanese junior officers and 170 U.S. Navy counterparts met yesterday in a "symposium" in Hawaii. The theme of the symposium was the 50th anniversary of the signing of the U.S.-Japan Treaty of Mutual Cooperation and Security of 1960.

Three Japanese ships, the Kashima, Yamagiri and Sawayuki, were in port here.

Japan and the U.S. agreed to work out by the end of August the relocation of the U.S. Marine Corps’ Futenma Air Base on Okinawa, a point of contention for some Okinawans.