SINGAPORE - Prime Minister Lee Hsien Loong and Minister for Foreign Affairs Vivian Balakrishnan have written to the leaders of Vietnam to extend their deepest condolences on the passing of former Prime Minister Phan Van Khai.

Mr Khai, a Soviet-trained economist, held office for nine years starting in 1997. He died on Saturday (March 17) at the age of 84.

In his letter on Tuesday to Vietnam's Prime Minister Nguyen Xuan Phuc, PM Lee said that Mr Khai was instrumental in accelerating economic reforms in Vietnam when he was prime minister.

He added that Mr Khai had contributed greatly to the close relations between Singapore and Vietnam.

"The Connectivity Framework Agreement, which underpins the multi-faceted cooperation between our countries, was first mooted during his official visit to Singapore in March 2004," PM Lee said.

"I recall the warm hospitality that Mr Khai accorded to me when I made my introductory visit to Vietnam as Prime Minister in December 2004."

In a separate letter to Vietnam's Deputy Prime Minister and Minister of Foreign Affairs Pham Binh Minh, Dr Balakrishnan called Mr Khai a "good friend of Singapore", who oversaw one of Vietnam's fastest and most stable economic growth periods during his nine years as prime minister, and helped further closer relations between Singapore and Vietnam.

"His contributions to Vietnam's development and the partnership between our countries will be remembered long after his passing," Dr Balakrishnan added.