SINGAPORE - President Tony Tan Keng Yam and Prime Minister Lee Hsien Loong have written to Phillippine President-elect Rodrigo Duterte to congratulate him on his recent election victory.

The Philippine Congress on Monday (May 30) officially proclaimed Mr Duterte as the nation's next president.

In his letter on Monday, Dr Tan noted that Singapore and the Philippines are "old friends with strong ties", with both countries cooperating closely on Asean and international matters to promote peace, stability and prosperity.

Dr Tan added that he and his wife were impressed by the economic progress of the Philippines during a state visit in April 2014, highlighting the resilience of Tacloban residents in the aftermath of the devastating Typhoon Yolanda.

"I am confident that you will lead the Philippines economy to greater heights," he wrote. "I wish you success as you embark on your new role, and look forward to meeting you soon. I would also like to take this opportunity to invite you to visit Singapore at the earliest opportunity."

Mr Duterte, 71, will be sworn into office on June 30. The Davao city mayor received nearly 39 per cent of the vote at the country's presidential election earlier this month.

In his letter, PM Lee said the strong mandate reflects the trust that Filipinos have in Mr Duterte's leadership and vision.

He wrote: "Singapore and the Philippines share close ties spanning many sectors, including trade and investment, culture and people-to-people exchanges. Our bilateral relationship will reach a milestone in 2019, when we celebrate 50 years of diplomatic ties."

PM Lee noted that Singapore is looking forward to the Philippines' Asean chairmanship next year.

"I am confident that we will be able to foster closer Asean integration amid a complex and fast-changing global landscape," added PM Lee, who wished Mr Duterte good health and success in his new position.