The Boston attack is the second deadly bomb strike against a marathon, according to the Global Terrorism Database, with 14 people killed in a suicide attack at a Sri Lankan event in 2008.
Among the dead in the attack at Weliweriya, near Colombo, were a government minister, and a runner in the 1992 Olympic marathon, K.A Karunaratne.
The bomb, attributed to the Tamil Tiger rebels, was detonated at the marathon starting line as the Minister for Highways, Jeyaraj Fernandopulle, prepared to begin the race.
He was among those killed, while more than 90 people were injured.
"There was a sound of huge explosion and I saw a fireball," said Nishan Priyantha, a local journalist, told the Associated Press at the time.
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Another witness described the carnage resulting from the blast as “horrible”.
