Prime Minister Lee Hsien Loong on Wednesday signed the condolence book for the late Vietnamese President Tran Dai Quang at the Vietnamese embassy.
In his condolence message, PM Lee said Mr Quang, who died at age 61 last Friday after a prolonged illness, "dedicated his life to serving his beloved country, improving the lives of Vietnamese and raising Vietnam's standing in the world".
"He also supported closer cooperation between our two countries, and will always be remembered as a good friend of Singapore."
Deputy Prime Minister Teo Chee Hean attended Mr Quang's state funeral in Hanoi on Wednesday. Said DPM Teo in a Facebook post that day: "I have known President Quang for many years. We met many times and fondly recall him and his wife, Madam Nguyen Thi Hien, hosting us in his beautiful hometown of Ninh Binh.
"Quang strengthened the Vietnam-Singapore strategic partnership. My deepest condolences to Madam Hien and the family. Vietnam has lost a leader, and I will miss a good friend."
Mr Quang, a member of the ruling Communist Party's powerful politburo, spent more than four decades climbing the ranks of the security apparatus until he became president in 2016.