Modi first called up Sirisena and then wrote a letter to him, hailing his win and expressing India's continued solidarity to Sri Lanka's peace and development.
"I spoke to Shri Maithripala Sirisena and congratulated him. I congratulate the people of Sri Lanka on the peaceful and democratic poll process," he tweeted. "As a close friend and neighbour, reaffirmed India's continued solidarity and support for Sri Lanka's peace, development and prosperity," the PM added.
In the letter, Modi wrote, "Your historic victory is a tribute to your vision for Sri Lanka and your capacity to connect with people's yearning for change." He said he looked forward to working with him "to take our relationship to a new level for benefit of our people and our region."
Modi wished Sirisena all the success in building a peaceful and prosperous Sri Lanka, on foundations of genuine and effective reconciliation.
The PM also invited Sirisena to visit India, saying he looks forward to receive him in India.
Sirisena defeated Mahinda Rajapaksa in the elections held on Thursday.
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