BEIJING (REUTERS) - China's top anti-graft agency has opened an investigation into former China Telecom Corp Ltd vice president and chief engineer Leng Rongquan, a 20-year executive and Communist Party member who retired in 2010.

Leng is being probed on "suspicion of serious violations of the law", according to a brief statement by the Communist Party's graft watchdog, the Central Commission for Discipline Inspection (CCDI).

The CCDI did not provide additional details about Leng's suspected activities but "serious violations of the law" usually connotes graft.

China Telecom could not immediately provide comment on the investigation when reached late on Friday.

China's anti-corruption investigators pledged earlier this year to begin scrutinizing telecom giants China Mobile Ltd and China Telecom Corp Ltd after an ongoing probe into China Unicom Hong Kong Ltd ensnared several high-ranking executives.

The CCDI said it examined more than 50,000 cadres in 2014 alone, although investigations targeting an executive who has been retired for five years, as in Leng's case, have been relatively uncommon.

After completing sweeps of central and provincial governments last year, the CCDI said it would turn its attention to China's vast state-owned enterprises, which have long been plagued by underperformance despite reform efforts by central leaders.