A team of Japanese searchers has discovered 51 remains in two areas listed by the U.S. military after the war as enemy cemeteries, one of which could contain as many as 2,000 bodies, Japan’s Kyodo news agency said Friday.

The team was to report its findings later Friday to the prime minister’s office.

Officials at Japan’s health ministry, which supervises search efforts on the remote island, confirmed that 51 bodies had been recovered and two sites believed to be burial grounds had been found. But they could not immediately confirm the potential size of the mass graves or other details of the Kyodo report.

The discovery of the remains would be one of the biggest breakthroughs in decades toward finding the bodies of roughly 12,000 Japanese who remain missing and presumed dead after the 1945 battle on the island, which has been renamed Iwoto by the Japanese government.

The island was seen as key to the United States because it had an early warning radar station and three airfields used by Japanese fighter planes that posed a threat to U.S. bombing raids on Tokyo and Japan’s main islands. The U.S. wanted the airfields for its fighter escort planes.

Virtually all of the 22,000 Japanese soldiers tasked with defending the rugged, volcanic crag were killed in the battle, which became a symbol and rallying point for the United States in the Pacific war after the U.S. flag was raised on its highest ground, Mount Suribachi.

The battle claimed 6,821 American and 21,570 Japanese lives. Dozens of remains are recovered every year, but about 12,000 Japanese are still classified as missing in action and presumed killed on the island, along with 218 Americans.

Fighting began on Feb. 19, 1945, but Iwo Jima was not declared secured until March 26.

Japan surrendered in August of that year, after the atomic bombings of Hiroshima and Nagasaki.

According to the Kyodo report, searchers dug near a runway at a base used by the Japanese military — the only full-time inhabitants of the island — and at the foot of Suribachi. It said the operation began early this month based on information from the U.S. National Archives and Records Administration.

The report said the main site is estimated to have about 2,000 bodies and the Suribachi site 70-200 bodies. It said the recovery effort was expected to take several months.