TOKYO—Japan has decided to divert some of its gas reserves to Europe amid growing concern over possible disruptions of supplies due to the Ukraine crisis, Economy, Trade and Industry Minister Koichi Hagiuda said Wednesday. The decision was made at the request of the United States and European Union and is intended to help European countries cope with uncertainties about gas supplies given fears of a possible Russian incursion into Ukraine, he said after meeting with U.S. Ambassador Rahm Emanuel, who arrived in Japan in late January. Emanuel welcomed Japan’s offer. “Japan’s assistance to Europe is an example of how President Biden and Prime Minister Kishida are working closely together with like-minded partners to deter Russian aggression against Ukraine, and uphold our shared values,” Emanuel said in a statement. Russia is the third-largest oil producer after the United States and Saudi Arabia and the source of about 40 percent of the …