BEIJING A festering territorial dispute between China and Japan threatened to escalate on Friday after Beijing condemned Tokyo's decision to allow a Japanese company to explore for gas in the East China Sea. "This act by Japan is a grave provocation and violation of China's sovereign rights," a Chinese Foreign Ministry official in charge of Asian affairs, Cui Tiankai, told the Japanese ambassador to China, Chihiro Atsumi, who had been summoned to receive the official protest, the official Xinhua news agency reported. The Chinese Embassy in Tokyo also lodged a formal protest with the Japanese Foreign Ministry, Xinhua reported. China...