A senior Japanese government official said he saw strong links between the recent alleged incursion of a Chinese nuclear submarine into Japanese waters and China's exploration for natural gas reserves in disputed maritime territory. Shoichi Nakagawa, Japan's Minister of Economy, Trade and Industry, said he believed the incident was linked to an ongoing row over energy reserves near the Senkaku islands – known as the Diaoyu in Chinese. The submarine incursion sparked Japan's first nationwide naval alert in several years. Following a two-day chase in the East China Sea, officials said they had identified the sub as Chinese and demanded an apology from Beijing. Chinese officials have made no comment other than to say the matter was being investigated. The two sides held talks last month on the disputed gas exploration projects, but they ended without agreement.