The Japanese Self-Defense Forces and the U.S. military on Thursday began a large-scale joint exercise mainly in and around Japan's southwestern islands, in an effort to boost their operational capability in those areas, with China's intensifying military activities in mind.The exercise, called "Keen Sword," is scheduled to last until Nov. 19 and will involve about 26,000 personnel from the Japanese ground, maritime and air self-defense forces and around 10,000 U.S. soldiers, including those from the Space Force, according to the Japanese Defense Ministry.From Japan and the United States, some 20 and 10 vessels and about 250 and 120 aircraft will take part, respectively, according to the ministry.Tokyo and Washington have been increasingly concerned about Beijing's maritime assertiveness in the Indo-Pacific region, including Chinese vessels' repeated intrusions into Japanese territorial waters near the Senkaku Islands.China has also intensified military activities near Taiwan, a self-ruled democratic island which the communist country regards as a breakaway province to be reunified with the mainland, by force if necessary."