The powerful blast occurred during the morning rush hour directly in front of a police building in the tightly-guarded town of Vavuniya, 258 kilometres (160 miles) north of the capital Colombo, the defence ministry said. The wounded, some of them schoolchildren, were rushed to the main hospital, doctors said.
"It was a Tiger suicide bomber who rammed his (explosives-packed) motorcycle as policemen were leaving for duty," military spokesman Udaya Nanayakkara said.
"All those killed in the attack were police personnel," police spokesman Ranjith Gunasekara said, identifying the victims as nine policemen and three female constables.
Sri Lanka's military retaliated with a string of air attacks on rebel targets inside guerrilla held-territory north of Vavuniya, defence sources said. They said jet aircraft bombed a store house of the Tamil Tigers in Mullaitivu district while Mi-24 helicopter gunships attacked Tiger bunkers in the northern peninsula of Jaffna. There were no immediate reports of casualties in the air attacks and there was also no immediate reaction from the guerrillas.Vavuniya is a de facto frontier town bordering territory further north held by the rebels, who are fighting for a separate Tamil homeland in the majority Sinhalese island.