The first possible casualty of Friday's shock vote to impeach South Korean President Park Geun-hye emerged Saturday as Japan's top government spokesman hinted that a trilateral summit with Seoul and Beijing was unlikely to be held this year.

"The situation is becoming extremely tough for holding the summit within the year," Chief Cabinet Secretary Yoshihide Suga was quoted by Kyodo News as saying on Saturday.

The summit, which Tokyo had planned to host sometime around Dec. 19, was to bring together Park and Chinese Premier Li Keqiang on their first trips to Japan.