Singapore's first and longest-serving prime minister, Lee Kuan Yew, died Monday, the prime minister's office said. He was 91.

"The Prime Minister is deeply grieved to announce the passing of Mr. Lee Kuan Yew, the founding Prime Minister of Singapore. Mr. Lee passed away peacefully at the Singapore General Hospital today at 3:18 a.m.," the office said in a statement released early Monday morning.

Lee, who ruled Singapore from 1959 to 1990, is credited with transforming it from a colonial backwater into one of Southeast Asia's most advanced and prosperous economies during his three decades in power.