A file photo of former assistant foreign minister of China, Zhang Kunsheng. [Photo: Weibo]

Former assistant foreign minister Zhang Kunsheng has been put under investigation for graft, the Supreme People's Procuratorate said in a statement on Tuesday.

The statement said Zhang is subject to "coercive measures" -- which may include summons by force, bail, residential surveillance, detention and arrest.

Zhang was expelled from the ruling Communist Party of China earlier this month. A report filed at the time said he was found to have flouted Party codes of conduct by joining private clubs, accepting gifts and money and trading power for sex.

He also used his post to seek benefits for other people, and is suspected of accepting bribes for these favors, the CPC Central Commission for Discipline Inspection said then.