COLOMBO, Sri Lanka (CNN) -- A bomb exploded on a crowded commuter train in a southern suburb of Sri Lanka's capital Monday, killing nine people and wounding at least 72 others, police said.
The Sri Lanka military was already on high alert after three bombs were found before the blast.
The parcel bomb had been placed in the luggage rack on the train, which was bound for the southern town of Panadura, 27 kilometers (17 miles) from Colombo, police said.
Investigators blamed the country's Tamil Tiger separatist movement for the attack, which occurred about 5:30 p.m. (1200 GMT, 0800 ET) in the southern suburb of Dehiwala.
Many of those on the train were office workers headed home at the end of the workday, police said.
The bombing came amid a nationwide alert triggered by the discovery of at least three packages, in three different towns, that contained bombs.
It followed allegations by the Tamil Tigers, who are fighting for an independent Tamil homeland in northern Sri Lanka, that government forces had killed 16 civilians in an attack on rebel-held territory in the Wanni region Friday.
The rebels also said the government killed an infant and a 17-year-old girl when warplanes bombed the area the same day.