Sri Lanka's former wartime defence chief Gotabaya Rajapaksa has won a presidential election that has split the country along ethnic lines.

Official results showed Mr Rajapaksa, 70, took 52.25% of the vote. His rival Sajith Premadasa had already conceded. Mr Rajapaksa was the clear victor in Sinhalese majority areas while Mr Premadasa scored better in the Tamil-dominated north.

The election is Sri Lanka's first since the deadly Easter Sunday attacks.

Militants linked to the Islamic State group targeted churches and high-end hotels across the island in April, killing more than 250 people. As a result, national security was seen as a dominant issue ahead of the vote.

Mr Rajapaksa, who has positioned himself as a strong figure who can assure Sri Lankans' security, is a highly controversial figure among the country's more than two million Tamils.

He and his brother Mahinda Rajapaksa, the former president, spearheaded the defeat of separatist Tamil Tiger rebels in 2009, ending a decades-long war in which at least 100,000 people died.