World leaders paid tribute to Lee, describing the former prime minister as a powerful figure who had earned his place in modern history as a revered leader. Singapore's transformation from a British colonial backwater to one of the world's leading financial hubs is widely attributed to his leadership.

Lee was a "true giant of history," US President Barack Obama said in a statement following news of his passing.

"His views and insights on Asian dynamics and economic management were respected by many around the world," Obama went on to say. "No small number of this and past generations of world leaders have sought his advice on governance and development."

UN Secretary-General Ban Ki-moon said he was "deeply saddened" by Lee's death.

"[Singapore's] founding father will be remembered as one of the most inspiring Asian leaders," Ban said in a statement.

Lee Kuan Yew passed away early Monday morning at the age of 91. He had been hospitalized on February 5 with severe pneumonia.

Singapore's "founding father" began his political career in 1954 when he co-founded the People's Action Party (PAP). Five years later he became the city-state's first prime minister, an office he held until 1990. During his tenure, he was credited with a strict rule that laid the groundwork for a stable nation with a booming financial sector and a low crime rate. Singapore is one of the world's richest countries on a per capita GDP basis.

The city-state's government announced seven days of national mourning following his death. His funeral is to take place on Sunday.

UK, Malaysia pay tribute

Relations with both the United Kingdom and Malaysia influenced Lee's political career. After declaring independence from British colonial rule in 1963, Lee brought the city into a federation of states which eventually became Malaysia. However, by 1965 Malaysia released Singapore from the political band over ideological differences.

Despite the potential for turbulent diplomatic ties, leaders from both countries testified to Lee's legacy as a steadfast international partner.

"He was always a friend to Britain, if sometimes a critical one, and many British prime ministers benefited from his wise advice, including me," said UK Prime Minister David Cameron.

Malaysian Premier Najib Razak pledged to maintain good ties with his southern neighbor.

"I pay tribute to Mr. Lee Kuan Yew's determination in developing Singapore from a new nation to the modern and dynamic city we see today," Razak said.

"His achievements were great, and his legacy is assured," he added.

HRW calls for reform

Not all condolences praised the Asian leader. Human Rights Watch pointed to Lee's human rights record in light of his silencing of political dissent and implementation of harsh punishment for minor infractions.

Lee's "tremendous role in Singapore's economic development…came at a significant cost for human rights," HRW Deputy Asia Director Phil Robertson told DW.

On behalf of the human rights group, Robertson urged Singaporeans to move forward and pursue more justice for freedom of speech and "political liberalization" away from a one-party system.

"Now that Lee Kuan Yew has passed from the scene, perhaps that long overdue conversation can finally proceed," he said.

Lee's oldest son, Lee Hsien Loong, is currently Singapore's premier.

kms/cmk (AP, AFP, Reuters, dpa)