Japan has notched up seven straight quarters of economic growth -- the longest positive run for 16 years -- with the upcoming 2020 Olympic Games giving the economy a shot in the arm. But it has struggled to achieve the 2.0 percent inflation rate thought crucial to boosting the world's third-largest economy. Government data released Friday showed the core inflation rate was up 0.5 percent last year following a 0.3 percent fall the previous year. "The rate was largely sustained by energy prices as consumer buying sentiment remains weak," said Yosuke Yasui, senior economist at the Japan Research Institute. "It is still very difficult to achieve the two-percent target," Yasui told AFP. In December alone, the core inflation rate rose 0.9 percent from a year earlier, the 12th straight year-on-year gain, the internal affairs ministry said. That met market expectations, according to data compiled by Bloomberg News. When volatile fresh food and energy were stripped out, prices rose by even less -- just 0.3 percent in December, the ministry said. Japan has battled deflation for many years and the central bank's ultra-loose monetary policy appears to be having limited impact. The bank has signalled it has no plans to exit the policy, despite moves in that directions in other major economies.