On Monday, the Japan Ground Self-Defense Force confirmed the deaths of two male crew members recovered by special divers from the 100-meter (330-foot) -deep seabed where they were found with the wreckage and three other crew members. The other five crew members on board at the time of the crash are still missing.?

The UH-60JA Black Hawk helicopter disappeared April 6 soon after taking off from an army base on Miyako Island for a reconnaissance mission in Japan's southern islands.

Prime Minister Fumio Kishida on Monday expressed his “deepest regret” over the deaths Monday and pledged to do the utmost for the recovery of the rest of the crew members “so that those who devoted their lives for the defense of the country can go back to their families as soon as possible, while we pursue our effort to find the cause of the accident.”

Officials are studying ways to lift the aircraft to find the cause of the crash.

An unused lifeboat, a door, and other fragments believed to be from the helicopter were found but the army has had trouble locating the aircraft in the area's coral-rich deep sea.

Japan is aggressively building up its defense capability in its southwestern islands in response to China's increasingly assertive military activity in the region, including near Taiwan.

The helicopter was stationed at a key army base in Kumamoto prefecture on Japan's southern main island of Kyushu, according to the Defense Ministry. One of its 10 crew members was Lt. Gen. Yuichi Sakamoto, who was just promoted to division commander at the end of March.

The army said the helicopter had a routine safety inspection in late March. No abnormality was found during its subsequent test flight nor on its trip from its home base of Kumamoto to the Miyako island, about 1,800 kilometers (1,120 miles) southwest of Tokyo.

Japan started deploying the Black Hawk, a twin-engine, four-bladed utility helicopter developed by US manufacturer Sikorsky Aircraft and produced by the Mitsubishi Heavy Industry, in 1999 for rapid response, surveillance and disaster relief missions.