They expressed confidence that Datuk Seri Najib, 55, who took over from Tun Abdullah Ahmad Badawi, at a time when Malaysia is facing a most challenging time, will be able lead the country to greater heights.

In his letter, PM Lee said: 'You have served Malaysia for many years before becoming Prime Minister. I am confident that Malaysia will continue to prosper under your stewardship.

'Malaysia-Singapore relations are multi-faceted. Our countries are connected by history, geography and family ties. We share common interests in many areas, not least in keeping our economies and region stable during this global economic crisis.

'We have much to gain by working together bilaterally, regionally and internationally. I look forward to working closely with you to further enhance our warm relations and mutual cooperation.'

Mr Lee said he and his wife Ho Ching welcome Datuk Seri Najib and his wife Datin Seri Rosmah to Singapore soon on their introductory visit.

Senior Minister Goh Chok Tong, in his letter to the Malaysian PM, said: 'You are taking over the leadership of Malaysia at a most challenging time, both externally and internally.

'Reading your recent statements on the need for change and your wish to be judged by your actions, I am confident Malaysia will overcome its challenges under your strong leadership.'

Minister Mentor Lee Kuan Yew said of Datuk Seri Najib's appointment: 'Your father, Malaysia's second Prime Minister, held the office with great distinction. He would have been very proud of you, were he still alive. You now have the opportunity to lead Malaysia to greater heights.'

Senior Minister and Co-ordinating Minister for National Security Prof S Jayakumar and DPM Wong Kan Seng also sent congratulatory letters to the new Malaysian leader.

PM Lee, SM Goh, Prof Jayakumar and Mr Wong also sent valedictory letters to Tun Abdullah praising him for his efforts to bring progress to Malaysia and improving ties with neighbouring countries.