The health condition of Singapore's founding father and long-serving former leader Lee Kuan Yew, who has been in hospital with severe pneumonia for nearly six weeks, has worsened, the government said on Tuesday.

Lee, 91, is being treated at downtown Singapore General Hospital where he has been on a ventilator. At the end of last month, officials said his condition was improving, but further statements said there had been no change.

"Lee Kuan Yew's condition has worsened due to an infection. He is on antibiotics. The doctors are closely monitoring his condition," the office of Prime Minister Lee Hsien Loong, the founding leader's eldest son, said in a short statement.