SINGAPORE - Prime Minister Lee Hsien Loong has written to Chinese Premier Li Keqiang on Wednesday (July 24) to convey his condolences on the passing of former premier Li Peng.

Mr Li died just before midnight on Monday of unspecified illness, Chinese state media announced on Tuesday. He was 90.

"On behalf of the Government of the Republic of Singapore, I extend my deepest condolences to the Government and people of the People's Republic of China on the passing of former Premier Li Peng," Mr Lee wrote in his letter.

"Mr Li had served in senior leadership positions during a time of rapid economic and social change and great challenges for China," Mr Lee noted, adding that under Mr Li's leadership in the early 1990s, "China experienced dramatic economic development, as it implemented the policy of reforming and opening up, improving the lives of millions of Chinese people."

Mr Li served as Chinese premier from 1987 to 1998, and as chairman of the National People's Congress - China's Parliament - from 1998 to 2003.

A Russian-educated engineer by training, the former leader was one of the longest-serving members of the Communist Party's Politburo Standing Committee, the pinnacle of power in China, serving three five-year terms until 2002.

Mr Li notably visited Singapore in August 1990, near the tail-end of the Cold War and following the normalisation of relations between China and Indonesia.

Then Prime Minister Lee Kuan Yew had praised this as a positive development for the region, and said Singapore hoped to also establish diplomatic relations with China in the coming months.

The two countries officially formalised diplomatic ties that October.

Mr Lee noted that as Premier, Mr Li oversaw the establishment of Singapore-China diplomatic relations in 1990 and promoted friendship and cooperation between the two countries.

"Mr Li was the first Chinese Premier to visit Singapore. He promoted cooperation between Singapore and China in many areas, ranging from economics to culture and education. He also witnessed key milestones in our bilateral relations, especially the launch of the China-Singapore Suzhou Industrial Park, our first Government-to-Government project," Mr Lee added.

Mr Lee further noted that Mr Li also played an important role in strengthening relations and cooperation between Asean and China.

"Under Mr Li's leadership, China established diplomatic relations with many Asean Member States, and the Asean-China dialogue partnership. This laid the ground for the close cooperation between Asean and China today."

"Mr Li will be deeply remembered. Our thoughts are with the people of China," Mr Lee wrote.

Mr Li is survived by his wife Zhu Lin and three children, elder son Li Xiaopeng, only daughter Li Xiaolin, and youngest son Li Xiaoyong.