More than a month after Taiwan's envoy to Japan resigned his post, Taiwanese President Ma Ying-jeou faces a dearth of candidates he can trust to appoint as de facto ambassador to Tokyo, revealing yet another stumbling block in bilateral relations, experts said.

"There just aren't enough choices — there's nobody, really," said George Tsai, an international affairs expert at Taiwan's Chinese Culture University, explaining why the appointment process has dragged on.

Koh Se-kai, the last top envoy, resigned July 10 in the midst of a diplomatic row between Taipei and Tokyo over a boat collision in disputed waters.