Prime Minister Lee Hsien Loong was among several leaders who congratulated Malaysia's Prime Minister Mahathir Mohamad, who was sworn in on Thursday.
PM Lee spoke to Tun Dr Mahathir over the phone yesterday, and said in a Facebook post after their call: "He was busy meeting people for his Cabinet appointments!"
Mr Lee shared a photo of the both of them taken nearly 20 years ago, which shows him and Dr Mahathir at the Hari Raya Open House in Johor Baru in December 2001.
PM Lee said that he wished Dr Mahathir and his government all the best, and that he hopes to be able to catch up with Dr Mahathir in person, either in Kuala Lumpur or Singapore, very soon.
Dr Mahathir was sworn in as Malaysia's seventh prime minister on Thursday night, a day after his Pakatan Harapan coalition delivered a shock win at the Malaysia election, ending the six-decade rule by former premier Najib Razak's Barisan Nasional coalition.
In a statement on the call, Singapore's Ministry of Foreign Affairs said: "PM Lee said that he looked forward to working with PM Mahathir to further strengthen and deepen bilateral cooperation for the mutual benefit of both countries."
Indonesian President Joko Widodo also called Dr Mahathir to congratulate him, Mr Joko's office said. In a phone call on Thursday night, Mr Joko said he conveyed his appreciation for the smooth and peaceful election.
In their conversation, Mr Joko said he was confident that under Dr Mahathir's leadership, relations between their countries would continue to improve, and he hoped Dr Mahathir would always be in good health to carry out the mandate of the Malaysian people.
The White House press secretary said in a statement yesterday that United States President Donald Trump congratulated Dr Mahathir on his swearing-in.
"The President also congratulates all Malaysians on their participation in a competitive and peaceful election campaign," the statement read. "The United States-Malaysia relationship is rooted in longstanding and strong people-to-people ties, shared democratic values, and commercial relations. The US looks forward to continuing to work closely with Malaysia to further strengthen the United States-Malaysia comprehensive partnership, and to address common international and regional challenges," it added.