Insight: Japan unease over U.S. alliance adds fuel to Abe's security shift

Japan's Prime Minister Shinzo Abe addresses a session at the annual meeting of the WEF in Davos January 22, 2014. REUTERS/Ruben Sprich

TOKYO (Reuters) - In public, Japanese Prime Minister Shinzo Abe's government lists a more assertive China and a volatile North Korea as its top security concerns.

Behind the scenes, though, another concern is growing: that the United States may one day be unable or unwilling to defend Japan, interviews with Abe advisers, politicians and security experts show. The worries are adding momentum to Abe's drive to beef up Japan's air and naval forces while loosening constitutional limits on action its military can take abroad.