Deputy foreign minister in charge of economic affairs Shinichi Nishimiya died Sunday, three days after collapsing unconscious on a street in Shibuya district, Financial Times reports.

The newly appointed Japanese ambassador to China was scheduled to leave in mid-October to take his post as replacement to Uichiro Niwa. According to Takashi Ariyoshi, a ministry official, doctors were looking into the cause of death but they have as yet made no announcement as to the cause.

The unfortunate demise of the 60-year old career diplomat came amid escalating tensions between Japan and China over disputed islands in the East China Sea. Tokyo announced Tuesday it had nationalised three uninhabited islands from the chain, sparking violent protests across China, the latest of the string of backlashes in Beijing.

The Japanese embassy in Beijing was thrashed with eggs and plastic water bottles while several Japanese-owned department stores also came under attack. US Defense Secretary Leon Panetta warned that the ensuing tensions could eventually lead into warfare and appealed for “restraint”.