Vietnamese leader Nguyen Phu Trong, the architect of the Southeast Asian country's anti-corruption drive, has been suffering from an unspecified illness, four diplomatic sources have told Reuters.

Trong was admitted to the 108 Military Central Hospital in Hanoi, the diplomatic sources said, requesting anonymity because of the sensitivity of the issue in the communist-ruled country.

In the first official comments on the 75-year-old Vietnamese leader's health since his last public appearance 11 days ago, foreign ministry spokeswoman Le Thi Thu Hang said on Thursday that Trong's health had been affected by a "heavy workload" and "changeable weather conditions".

Hang did not say how serious Trong's condition was, but added that he would "resume his normal duties soon", without elaborating.