Japan lodged a protest with the United States on Tuesday over two forced landings by American military helicopters in the past few days in Okinawa, while U.S. Defense Secretary Jim Mattis apologized to his Japanese counterpart over the incidents.

"Frequent accidents amplify the local people's anxiety," Japanese Foreign Minister Taro Kono was quoted as telling U.S. Ambassador to Japan William Hagerty during talks over the phone, according to the Japanese government.

Kono told Hagerty that the Japanese government has "a serious concern" about the frequency of such accidents and incidents and called on the United States to take "fundamental measures" to prevent them.

Hagerty said the United States considers the safety of the local people the top priority and expressed his readiness to provide information quickly, according to the Japanese Foreign Ministry.

Earlier in the day, Japanese Defense Minister Itsunori Onodera made a similar request to Mattis during a teleconference. Mattis offered an apology and agreed to work on the issue, according to Onodera.

An AH-1 attack helicopter from the U.S. Marine Corps Air Station Futenma in Okinawa was forced to land at a waste disposal site in the village of Yomitan on Monday, just two days after a UH-1 helicopter, also from the base, made an emergency landing on a beach on Ikei Island in the city of Uruma.

Although the incidents resulted in no injuries, concerns were reignited among the local government and residents.

The incidents are the latest in a slew of accidents involving U.S. military aircraft in the southern Japanese island prefecture, which hosts the bulk of U.S. military facilities in Japan.

Last October, a CH-53E helicopter crash-landed and burst into flames, while a large window dropped from another helicopter of the same type into the playground of an elementary school in December, both on Okinawa's main island.

Okinawa Gov. Takeshi Onaga told reporters Tuesday, "I am really speechless. Nothing has moved forward (to prevent such incidents happening)."

Deputy Gov. Moritake Tomikawa told senior Japanese defense and foreign ministry officials to urge the U.S. military to take effective preventive measures.

The AH-1 helicopter made what the U.S. military called a precautionary landing at the site, about 250 meters from a hotel, at about 4:45 p.m. Monday and the aircraft's two crew were unhurt. The aircraft took off and flew to the Futenma base on Tuesday morning.

According to the Japanese Defense Ministry's local bureau, the U.S. military said Tuesday that the crew saw a warning light regarding its tail rotor system and decided to make a landing to avoid an accident.

Senior officials of the Okinawa prefectural government are considering demanding the Japanese government and the U.S. military to ground all AH-1 and UH-1 helicopters for inspections until the causes of the incidents are identified.

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