Lee, who turned 63 on February 10, has been diagnosed with prostate cancer and will undergo a surgery on Monday.

"Dear @leehsienloong, hoping you have a successful surgery & a quick recovery. My good wishes to you," Modi tweeted late Sunday.

This is the second time that Lee has suffered cancer. The latest bout is unrelated to the lymphoma that was first discovered in 1992 while he was deputy prime minister.

Prime Minister Lee had congratulated Prime Minister Modi on his Lok Sabha election victory on Twitter and Facebook.     

In response, Modi had hailed Singapore as a valued friend and expressed confidence that bilateral ties will become stronger.

Singapore is India's largest trade and investment partner in ASEAN, accounting for a third of India's overall trade with ASEAN.

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