Slips of the tongue have often cost Japanese politicians their jobs, with the latest being Fumiaki Matsumoto, who stepped down as Japan's Cabinet Office state minister on Friday for heckling during a parliamentary meeting the previous day.

When an opposition lawmaker took up a string of incidents involving US aircraft, including emergency landings of helicopters, in a question to Japanese Prime Minister Shinzo Abe, Matsumoto heckled by saying: "How many people died from that?" Kyodo News Agency said.

Japan's opposition parties lashed out against Matsumoto for downplaying the incidents.

At a House of Representatives Budget Committee meeting on Monday, Abe apologized "deeply" to Okinawa residents and the country in general, adding that the government will make efforts to reduce Okinawa's base-hosting burden and to handle other matters by boosting discipline.

Residents of Okinawa have been angered by the frequency of accidents and incidents involving aircraft from the US, which has a large military presence on the island, also a source of tension.

After conducting an independent investigation, the Japanese Defense Ministry announced last week that accidents or incidents involving US military aircraft in Japan more than doubled in 2017, increasing to 25 cases from 11 the previous year, Kyodo reported.

In the most recent case last week, an AH-1 attack helicopter made an emergency landing in Tonaki village, leading the Okinawa Governor Takeshi Onaga to call for a thorough investigation.

After years of negotiations with Washington, Tokyo is relocating US Marine Corps Air Station Futenma to the less populated Henoko coastal area of Nago city from a crowded residential area of Ginowan.

The airfield relocation is intended to put an end to safety issues caused by operations at the Futenma base. However, many people in and outside Okinawa including Onaga want the facility relocated outside the prefecture.

On Jan 19, the Okinawa Prefectural Assembly unanimously passed a protest resolution in the aftermath of successive emergency landings of US Marine Corps helicopters, Ryukyu Shimpo reported.

The local legislators issued a statement calling for the suspension of Marine Corps Air Station Futenma's operations by the end of February next year to ease the concerns of local residents.

This is the first time that the local legislature has stated a deadline to call for suspension of MCAS Futenma, Ryukyu Shimpo said.

The land used for the Northern Training Area－a US exclusive-use facility－in Okinawa was returned to the prefecture last year, the biggest transfer of property since the prefecture's reversion from the US to Japan in 1972.

With the return of the 4,000-hectare site, the share of Okinawa in the total acreage of US military facilities in Japan decreased to 70.6 percent from 74.5 percent, according to the Naha-based Okinawa Times.