Japan plans to ask all people arriving in the country from the United States to self-quarantine for two weeks, starting on Thursday.
People with fevers or other symptoms arriving by sea and air are to be tested for the new coronavirus at quarantine stations.
US residents of Japan voted in a Democratic Party presidential primary on Sunday that is being held in 44 countries and territories.
Ballot stations were set up in Tokyo, Osaka and Nagoya. Many people came to the polling station in Tokyo's Shibuya Ward when it opened at noon.
A team of US environmental experts has surveyed an area of northeastern Japan that was struck by a massive earthquake and tsunami on March 11 2011.
On Tuesday, a team from the Smithsonian Environmental Research Center visited a lagoon in Rikuzentakata City in Iwate Prefecture. The lagoon was connected to the sea after a massive tsunami.
Two chartered aircraft sent by the US government to evacuate American citizens from a quarantined cruise ship have arrived in Japan.
The planes touched down at Tokyo's Haneda airport at around 10:30 p.m. on Sunday. Workers in protective clothing were seen loading luggage onto the aircraft.
The Defense Ministry has launched an environmental survey on an island in southwestern Japan where it plans to relocate US military exercises.
About 20 people, including ministry officials, arrived at Mageshima island in Nishinoomote city, Kagoshima prefecture, on Tuesday morning. The ministry says they will first study the island's wildlife and vegetation.
Prime Minister Shinzo Abe says the Japan-US alliance is an immovable pillar for protecting world peace.
On January 19, 1960, the revised Treaty of Mutual Cooperation and Security was signed by Abe's grandfather, Prime Minister Nobusuke Kishi, and US President Dwight Eisenhower.
Japanese Defense Minister Taro Kono has said a liaison officer has started working at a US command center for a Self-Defense Force intelligence-gathering mission in the Middle East.
Kono attended an Upper House committee session on Friday about the mission aimed at ensuring the safety of Japan-related shipping operating in the region.
Some Japanese government officials are concerned that Washington may pressure Tokyo to pay significantly more for stationing US forces in Japan.
Bilateral negotiations on the cost will likely shift into high gear as early as this summer, with the current five-year agreement on the costs of supporting US forces due to expire in March 2021.
A senior US State Department official says the US government plans to discuss with Japan how to share overall defense responsibilities, in addition to the cost of keeping US troops in the country.
The current five-year agreement on the cost of stationing US forces in Japan will expire in March 2021. President Donald Trump's administration has asked Japan to significantly increase its share of the burden.
The governments of Japan and the United States will consider how to cooperate to deal with toxic chemicals detected in high levels around US bases in Japan.
Organic fluorine compounds, such as PFOS, have been detected near US bases in the southern prefecture of Okinawa and Tokyo's Yokota Air Base. The chemicals have been proved toxic in tests using animals.
Japanese Defense Minister Taro Kono has inspected a parachute drill by the Ground Self-Defense Force and the US military. The exercise is aimed at preparing for a possible attack on Japan's remote islands.
Kono visited Camp Narashino near Tokyo where the SDF's only parachute unit, the 1st Airborne Brigade, conducted this year's first exercise on Sunday.
Japan's Prime Minister Shinzo Abe says he will make further diplomatic efforts to help ease the tensions between the United States and Iran.
Abe told reporters on Thursday morning that Japan has strongly urged all the parties concerned to exercise restraint, and that his country values diplomacy based on self-control.