A staunch friend of Taiwan will take over this summer as the top U.S. diplomat in Taipei, three sources briefed on the matter have said, roughly coinciding with the island's new president taking office at a time of rising tensions with China.

Like most nations, the United States has no formal diplomatic ties with Chinese-claimed Taiwan, but is its most important international backer and arms supplier, to Beijing's anger. China has ramped up political and military pressure against Taiwan.

The sources, who spoke on condition of anonymity as they were not authorized to speak to the media, said that Raymond Greene, currently deputy chief of mission at the U.S. Embassy in Tokyo, will replace Sandra Oudkirk as director of the American Institute in Taiwan (AIT).